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Old 08-21-2005, 04:19 PM   #1 (permalink)
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Jet A vs Diesel

I defueled a Gulfstream G-IVSP last week and now have 340 gallons of crystal clean Jet-A fuel. All the info I've found on the internet shows several difference, but so far I've had not problems.

I'm wondering if anyone else has used this fuel in their trucks.

I am mixing two quarts of semi-synthetic 2-stroke oil for every 30 gallons of fuel. This is simply to keep the injectors lubed as required by the diesel fuel.

Only observation I've made is that my MPG indicator is 2 mpg shy of what it normally is. I've seen no real depreciation in power but can certainly tell the exhaust is much cleaner.

If you've tried this please post your findings and results.
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Old 08-21-2005, 04:34 PM   #2 (permalink)
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Re: Jet A vs Diesel

I have run a lot f Jet A in my 01 PSD with no problem. I add 8oz of marvel mystry oil per 40 gallon tank. Have not had any troubles
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Old 08-21-2005, 04:43 PM   #3 (permalink)
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Re: Jet A vs Diesel

Jet A is almost identical to Diesel #1 and kerosine. That's why you lost MPG - just like you would lose MPG with Diesel #1 or winter blend compared to straight Diesel #2.

Yes, Jet A is "dry" and needs a lubricity additive. Stanadyne makes a good one. http://www.dieselpage.com/add3.htm
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Old 08-21-2005, 06:36 PM   #4 (permalink)
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Re: Jet A vs Diesel

I used to be a GSE mechanic for a Major airline and we ran Jet A in everything, STRAIGHT OUT OF THE PIT, no additives what so ever. So I was supprized to see the need for lubrication with it. We never had a problem in any of our diesels,Guess I learned something here.
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Old 08-21-2005, 07:28 PM   #5 (permalink)
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Re: Jet A vs Diesel

So what is the difference with JP-5? in my line of work that is what gets run in the helicopters but it has been run in the Cat diesels when we were out of #2 even though Cat doesnt recomend it the Paxtman engines say it doesnt matter
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Old 08-22-2005, 12:02 AM   #6 (permalink)
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Re: Jet A vs Diesel

Could be the lubrication issue. Cats run heiu injectors, what do paxtman(sp?) have. Bosch types may not need the lub.

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Old 08-22-2005, 11:02 AM   #7 (permalink)
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Re: Jet A vs Diesel

Jet will have much higher sulphur levels. About 3000 ppm over 500ppm for on-road diesel. So you should change your oil sooner.

I do not know the effect of high sulphur fuels on EGR engines. Since the 7.3 doesn't have egr, we don't care. But the extra sulphur forms extra sulphur dioxide, an acid gas. Then this is recirculated in EGR engines. Could cause a problem?

My diesel farm tractor's manual suggests that lubricity can be raised by adding SAE 10 weight oil. Hard to find this stuff, let alone the non-detergent type. The synthetic 2 cycle oil sounds like a good substitute.

Kerosine has less energy per gallon than diesel. You should expect lower mileage.

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Old 08-22-2005, 11:15 AM   #8 (permalink)
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Re: Jet A vs Diesel

I am not sure that Jet 5 has been tested in our engines. I belileve Jet 5 should be a mixture of Kerosine and gasoline or benzine. Not a lot of gas but still a little. I'd probably let someone else test it, or a few someones before I would use it.
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Old 08-22-2005, 04:49 PM   #9 (permalink)
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Re: Jet A vs Diesel

I contacted Marketing Fuel Technical Service at Chevron
and asked my question. What I received back was a BOOK and here it is:

"In regards to your inquiry about whether Jet A can be run in a diesel engine, Chevron would never advise anyone to use a particular fuel in an engine that was not designed for that fuel. We would advise that the inquiry be made to the equipment (engine) manufacturer."

Remember, while there is only one basic Jet A species, there are several kinds of diesel - diesel No. 1 and diesel No. 2 (amongst others). Jet A is more like Diesel No. 1. Diesel No. 2 is the more common "diesel" fuel, since it is the fuel used by vehicles "on-road".

All of the fuels are products of the refining process. One of the main differences between them is their distillation boiling ranges. Diesel No. 2 has a higher (in temperature) boiling range and is more dense than Jet A and/or diesel No. 1 (both of which have lower densities and lower boiling range temperatures). A fuel which is less dense will have lower fuel economy (less BTU's per gallon). All of this is "besides the point" as far as the appropriateness of any of the three to perform in the engines that were designed for their use. If the engine manufacturer indicates the use of only one type of fuel, that is the fuel that should be used.

For further information please visit Chevron's INTERNET site at Chevron Corporation Home Page
There are some very informative publications at the site at http://www.chevron.com/chevron_root/prodserv (there is an "underscore" character after the second "chevron" word). When you reach that site, click on the word "Fuels" and you will then see a "Publications" option.

That said, we will break down your inquiries into a group of statements that we have put together to answer others who have asked similar questions:

Jet A, Diesel No. 1, and Diesel No. 2, are covered by different American Society For Testing and Materials (ASTM) specifications. The diesel fuels are covered by ASTM D 975, "Standard Specification for Diesel Fuel Oils". Jet A has the designation of ASTM D 1655, "Standard Specification for Aviation Turbine Fuels".

According to the ASTM specifications listed above, the sulfur limit for Jet A is a maximum of 0.3 mass %. Because of an Environmental Protection Agency 1993 regulation, the specification for sulfur in "on road" Diesel No. 1 and Diesel No. 2 is a maximum of 0.05 mass % - a large difference from the Jet A sulfur level.

The EPA regulation would be broken if one were to use Jet A for "on-road" Diesel. Jet A is also not taxed for "on-road" use, so would be illegal to use in "on-road" vehicles and possibly illegal in some "off-road" uses as well. Both the sulfur level and the tax issue need to be considered in a legal sense when considering the uses of these fuels.

Another difference between the fuels is the viscosity. The ASTM D 1655 detailed viscosity requirement of Jet A is a maximum of 8 mm2/S (millimeter squared/Seconds - [1mm2/S = 1 Centistoke]) at -200C. The ASTM D 975 viscosity requirement of Diesel No. 1 is a minimum of 1.3 and a maximum of 2.4 mm2/S at 400C and of Diesel No. 2, a minimum of 1.9 and a maximum of 4.1 mm2/S at 400C. It is hard to compare these, since the testing temperatures of the diesels do not agree with that of the Jet A. However, the viscosities at 200 Centigrade and in units "milliPascal/Seconds" (still another, and different unit measurement) for the two fuels according to a national average of four semiannual surveys taken from 1990-1992 are as follows:

Jet A & Diesel No. 1 1.33
Diesel No. 2 3.20

Jet A and Diesel No. 1 tend towards lower viscosities. Lower lubricity is likely as the viscosity decreases. While this may not cause catastrophic instant damage, it could cause long-term wear of pumps, etc.

Jet fuels have additional specifications that aren't required of diesel fuels. A couple examples of these are the requirement of testing for certain components and a volatility requirement. Some of the methods for testing also vary from one fuel to the other. Basically, however, we have pointed out the biggest differences. If you need more detailed comparisons, please contact the ASTM society at their headquarters at 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428. They could provide you with copies of the specifications. Their phone number is 610-832-9500.

Once again, we stress that you should contact the equipment manufacturers and ask what fuels are proper for use in the engines you are curious about. Also, you must make certain you are not breaking any legal regulations."

So the bottom line is that although Jet-A may not cause immediate damage to a diesel engine and may allow the engine to run OK, its use may cause premature wear or fouling of the fuel system, and you may be breaking EPA regulations as well as not paying appropriate taxes. Outside the US, differences in viscosity still mean that the use of Jet-A for Diesel No. 1
may cause early wear of the fuel system. Kind of like running 10 weight oil in a car designed for 30 weight. So how much risk are you willing to take, because no engine manufacturer or fuel supplier will take part of the risk?


Diesel vs Jet Fuel
A New Diesel Fuel Additive Requirement
ASTM D-975, the ASTM standard for diesel fuel, is being modified to include a specification on diesel fuel lubricity. Lubricity is the fuel quality that prevents or minimizes wear in diesel fuel injection equipment. Diesel lubricity is largely provided by trace levels of naturally occurring polar compounds which form a protective layer on metal surfaces. Refinery hydrotreating processes which reduce the sulfur content of diesel blend components also remove these polar compounds. As a result, most of the diesels produced by refineries to meet January 1, 2006 ultra-low sulfur diesel (ULSD) sulfur specifications will not have adequate lubricating properties to meet the new ASTM lubricity specification.
Baker Petrolite is a leading provider of diesel lubricity improvers, fuel additives that restore the lubricating properties of severely hydrotreated diesel fuels. These additives have traditionally been added at the refineries producing the fuels.

In 2004 some major U.S. finished fuel common carrier pipeline companies announced that they would not allow the transport of diesel fuels already treated with lubricity improvers. This is due to their concerns about “trail back” of the lubricity additive into jet fuel tenders following the additized diesel, which are not allowed to contain these additives. As a result, most lubricity additive usage in the U.S. will take place at fuel terminals.
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WHAT ABOUT FUELS?
There are six things to consider when comparing hydrocarbon fuels:
1. Volatility. In short, what's the fuel's propensity to vaporize. This effects the ability to easily mix the fuel with air and the fuel's tendency to vapor-lock. It also determines the pollution characteristics of the fuel where evaporative pollution is a concern.
2. Pre-ignition & knock resistance. Referred to as "Octane value." How much energy does it take to get the fuel burning - how much does it resist auto-ignition from compressive heat? Also, what is the rate of burn of the fuel (which affects the rate of pressure rise)?
3. Energy content. How much energy can be extracted from the fuel as a percentage of its volume or mass.
4. Heat of evaporation.
5. Chemical stability, neutrality, and cleanliness. What additives does the fuel contain to retard gum formation? Prevent icing? Prevent corrosion? Reduce deposits?
6. Safety
The first three factors are often confused and interrelated when, in fact, they measure three completely separate things. There is no natural collelation between them.
General rules:
Heavy fuels (diesel, jet): Low volatility, low knock resistance, high energy per volume
Light fuels (gasoline): High volatility, high knock resistance, low energy per volume
Note that gasoline, partially, makes up for its (relatively) low energy-per gallon by the fact that a gallon of gasoline weighs less (by about 15%) than a gallon of jet fuel.

HOW DOES THE OCTANE OF DIESEL AND/OR JET FUEL COMPARE TO GASOLINE?
Diesel and Jet fuel (along with kerosene) have, indeed, terrible octane numbers; typically about 15-25 "octane". They tend to ignite easily from high compression. Their use in a gasoline engine will quickly destroy the engine.
Diesel fuel is rated by its cetane number which is determined, like octane, by running the fuel in a test engine. Instead of heptane and iso-octane they use napthalene (cetane rating = 0) and n-cetane (cetane rating = 100). In total opposite to octane ratings, the higher the cetane rating the higher the fuel's propensity to knock!
Just as using a fuel with an octane number higher than necessary in a gas engine will gain you noting, using a fuel with a cetane number higher than necessary in a diesel engine gets you nothing. On the other hand, where using a fuel with too low an octane number in a gas engine will result in a damaged engine, using a fuel with too low a cetane number of a diesel engine will just result in a rough-running (or not running at all) engine with no damage.
WHAT'S THE DEAL WITH DIESELS?
Why can diesel engines tolerate a low octane fuel? In all gasoline engines, (including injected gasoline engines!) the fuel/air mixture is present in the cylinder the entire time the piston is travelling upward on its compression stroke. This means it could be ignited at any time whereas we only want it to be ignited when the spark plug fires, some time just before the very top of the stroke. Furthermore, we want a nice, even, steady, pressure rise in the cylinder as a result of ignition. This means that we want the flame-front to travel linearly from the source of ignition (the sparkplug) to the other side. We do not want combustion to occur randomly within the mixure as that may cause a too-rapid pressure rise which will throw off all our calculations about where the piston should be and when.
First, In a diesel engine there is NO fuel in the combustion chamber as the piston starts up on its compression stroke. Instead, fuel is injected at high pressure (up to 3000PSI!) into the combustion chamber at the exact moment when ignition is desired. In a diesel engine with a compression ratio of around 20:1 (compared to 7:1 for many modern gas engines), the heat of compression will have raised the combustion chamber temperature to arond 1000-1500F. The injection time takes about .002-.004 seconds during which the fuel spontanously ignites from the heat of compression at just the right time. Even so, a diesel fuel with too low a cetane rating may not ignite, or may ignite poorly - especially on cold days starting a cold engine.
The second critical difference is that Diesels are set up to burn the fuel in a slightly different way.
In a gas engine, you typically set it up so that the mixture is ignited before the piston hits the top of the stroke. What you're aiming for is for the mixture to be fully burned around the top of the stroke - thus combustion pressures are maximized at the top of the stroke and gradually fall off as the piston moves downward on the power stroke (and increases the volume in the cylinder). Diesels, on the other hand, are set up to inject fuel very close to the top of the compression stroke. The fuel spontenously ignites (auto-ignition) and, actually, knocks just like it does in does in a gasoline engine (hence the classic diesel "knocking"). The combustion pressures in the diesel increase evenly as the piston goes down. The net result is that the diesel piston "feels" a constant pressure on it as the piston travels from top dead center to bottom dead center whereas a normally operating gasoline engine piston "feels" a constantly decreasing pressure as it travels to the bottom of the stroke. The net result is that the diesel feels a lot lower PEAK pressure while the pressure is maintained over a longer period. The gasoline engine feels a much higher peak pressure which starts to fall off immediately as the piston travels downward. The implication, for the latter, is that it periodically operates very close to the capabilities of the base metals. Anything, such as knocking, which increases those peak pressures even more is apt to push beyond the capabilities of the base metals and result in engine damage.
Knock in a gasoline engine tends to occur at the end of combustion, when pressures inside the cylinder have reached, as a result of spark ignition, very high values - values high enough to auto-ignite the fuel.
Knock in a diesel engine happens at the beginning of combustion as a direct result of piston compression only. It is what allows further combustion as the piston moves downward. This continued combustion keeps the cylinder pressure constant as the piston moves towards BDC.
WHAT DOES A HIGH OCTANE VALUE MEAN, TO ME?
A high octane rating ensures that it takes a REALLY hot ignition source to ignite the fuel (such as a spark plug or the flame-front itself) and not just the rise in pressure & temperature that's a result of normal combustion. Note that the thermal rises in the cylinder are in direct proportion to the compression ratio of the engine (more below). The higher the compression ratio, the higher the octane of the fuel that's needed.
Again, if the mixture in a gasoline engine ignites before the spark plug fires, we call that "pre-ignition." Pre-ignition can damage an engine before you finish reading this sentence. To reiterate, what we're really concerned with is called "knock" and that's the spontaneous ignition of the fuel-air mixure ahead of the flame-front as a result of the rise in cylinder pressure caused by the onset of ignition (caused by the firing of the spark plug).
WHAT ABOUT AIRCRAFT?
Now, back to aircraft. We want to make aircraft engines with the following characteristics:
1. Very high power/weight ratio
2. Low specific fuel consumption (so we don't need to carry around heavy fuel)
The easiest way to do this, without involving lots of complex machinery that might fail and add weight, is to raise the compression ratio of the engine. An engine's efficiency is in direct proportion to its compression ratio. Unfortunately, raising the compression ratio means we need to protect against knock/detonation. How do we do this? We use high (100 octane) fuel!
Driving Fuelishly BY JAY LENO, Published on: April 16, 2002
Alternative, renewable and old--all attributes that keep Leno partial to his 1909 Baker Electric and its well-made, long-lasting batteries
People ask me what I think of cars that use alternative fuels. Naturally, I have an opinion. I had a chance to drive the new BMW 750hL dual-fuel hydrogen car. It uses some existing technology: an internal-combustion engine and conventional automatic transmission. But it also has two separate gas tanks, and a button on the dash that you press to switch the engine from gas to hydrogen power. BMW built its own hydrogen-filling station in Oxnard, Calif., which is kind of critical--the infrastructure for hydrogen fuel doesn't exist. Hydrogen isn't hard to make, though. In California, there are units out in the desert that convert sunlight into hydrogen. It's not perpetual motion yet, but it's truly a renewable source you will never run out of. And what comes out of the tailpipe is water that's pure enough to drink. You convert that to hydrogen and you use it again. That's pretty neat.
As far as electric cars go, the technology isn't really new. I have a 1909 Baker Electric that goes 110 miles on a single charge. A General Motors EV-1 goes maybe 120 miles. So in nearly 100 years we've only come 10 extra miles. You can take the Baker's Edison batteries, wash 'em out and use 'em again. They're beautiful-looking even though they're almost a century old.
Here's the problem I have with modern electric cars. Talk to tow truck operators and see if they'll tow one. When an electric car gets into an accident, you've got more than the usual problems, what with 300 volts running through it. Are they gonna want to tow this thing with busted wires? Let's say it catches fire. What's the fire department gonna do? I wonder what the AAA manual says?
Personally, I think the best alternative fuel is one we already have, but this country doesn't want to produce: No. 1 refined diesel fuel. Diesels are 30 percent more fuel-efficient than spark-ignition engines. And a gallon of diesel has 10 percent more energy than a gallon of gas. You go to Europe and you can get a VW Golf that gets something like 60 mpg. You could bring that over here and it would sell just fine. It runs best on ultralow sulfur content No. 1 diesel, which burns cleanly and is very similar to jet fuel. For some reason, we don't want to produce high-quality, commercially available desulphured diesel fuel in this country, though some experts say we will by 2006. Meanwhile, our diesel fuel is filthy. When I run aviation fuel in my jet motorcycle it burns clean. But if I use regular diesel, it chokes the people behind me to death.
As for hybrids like the Honda Insight and Toyota Prius, I think they have wonderful technology. For someone like me who likes to drive, the Honda is fine. I enjoy it. I mean, if I'm in a performance car, I want to get as much performance out of it as I can. But in an economy car, I want to drive with my socks on. You know, touch the pedals lightly and see how much economy I can get. Either way, I enjoy playing the game. But the VW turbodiesel does everything the Honda Insight does--maybe even better. The European model gets better mileage, but it's not sexy. It doesn't have that sleek little shape with the fender skirts. It doesn't look like the future.
Obviously, the last days of an old technology are always better than the first days of the new. The final steam cars, like the Doble, which would get a head of steam up in less than half a minute, were better than the first gas ones. Eventually, we'll get there.
How Do Thielert Diesels Do It?
By Peter Garrison
October 2004
One reader castigated me for not paying enough attention to Thielert diesels. Another inquired whether the just-certified Diamond TwinStar would have superior climb performance because of the great torque of its Thielert diesel engines. A critical mass of Thielert interest has evidently been reached.
Thielert GmbH is located at the small town of Lichtenstein in the former East Germany (not to be confused with the principality of Liechtenstein, wedged almost invisibly between Switzerland and Austria). The company produces, among other things, liquid-cooled geared turbo-diesel aircraft engines based on Mercedes automotive designs. A 1.7-liter, 135-hp four-cylinder is currently certified for retrofit to Cessna 172s and Piper Warriors originally equipped with the 160-hp Lycoming O-320 engine. The Austrian firm of Diamond offers its single-engine Diamond Star with one of the engines, and the upcoming TwinStar has two. More than a hundred Thielert-powered airplanes are now flying, and the company expects to certify a 4.0-liter, 310-hp V-8 this year.
It's unusual to offer an engine of lower power to replace one of higher. One wonders where the company gets the chutzpah to do it. The answer is that, at least in the 172 and the Warrior, performance is barely affected, gaining a little in some areas and losing a little in others. To understand how this can be so when the new engine is apparently much weaker than the old, we need to look at the characteristics of diesel and gasoline engines.
To start with, their combustion cycles are fundamentally different. The gasoline engine draws a fuel-air mixture into the cylinder, compresses it, and finally ignites it with a spark. The need to avoid spontaneous ignition (either pre-ignition or detonation) limits the compression ratio, while the need to ignite and burn the compressed mixture requires that the ratio of fuel to air remain within fairly narrow limits. An air throttle, linked to a fuel valve in injected engines, regulates power, while a mixture control allows fine adjustment of fuel flow in order to ensure a combustible, but not wasteful, fuel-air ratio.
The Thielert engines have no air throttle. Only engine speed regulates the amount of air they take in, while fuel flow controls their power output. Rather than a fuel-air mixture, only air is compressed by the rising piston. A very high compression ratio—18:1, more than double that of a typical unsupercharged aircraft gasoline engine—raises the temperature of the air in the cylinder (because the same amount of heat energy gets crammed into a much smaller volume of air) above the point at which hydrocarbon fuels ignite spontaneously. No timed spark is needed; fuel, sprayed into the cylinder under extremely high pressure as the piston reaches the top of its travel, burns regardless of the fuel-air ratio, which is always, by gasoline-engine standards, very lean. There is no harm, after all, in having excess air being present, just so long as there is enough oxygen to react with all of the hydrocarbons in the fuel. Jet engines, too, take in far more air than they use for combustion.
In their familiar roles as powerplants for generators, trucks and ships, diesel engines are typically designed to be slow-turning but to have a long stroke. The stroke, which is the distance the piston travels, is twice the crankshaft’s "throw"; the throw, in turn, is the maximum length of the lever arm against which the piston exerts its pressure. Long throws ensure that diesels yield plentiful torque. Since horsepower is the product of torque and engine speed, a slow-turning engine with lots of torque can work as hard (that is, produce the same horsepower) as a faster-turning engine with lower torque. Torque is naturally determined not by crank geometry alone, however, but also by the pressure in the cylinder during the power stroke and by the area of the piston (which is as much as to say the "bore" of the engine).
Although the 135-hp Thielert Centurion 1.7's weight, around 300 pounds, is similar to that of the 160-hp Lycoming O-320, its displacement is less than a third of the Lycoming's. It achieves its maximum power at 2300 prop rpm—3900 crank rpm—versus 2700 for the Lycoming.
While it is tempting to suppose that the key to the similarity in takeoff and climb performance between the Lycoming- and Thielert-powered versions of the 172 and the Warrior lies in the diesel's superior torque, in fact both engines deliver about the same torque—around 300 pound-feet—to the propeller. I suspect that the explanation is really more mundane. The Thielert engine uses an automatic variable-pitch propeller, whereas the Lycoming, in these airplanes, drives a fixed-pitch prop. During takeoff and climb, the Lycoming does not achieve maximum rpm, whereas the Thielert does. The superior aerodynamic efficiency of the Thielert's propeller nearly erases whatever residual power advantage the Lycoming might have, and so the takeoff distance and rates of climb for the two engine types turn out to be quite similar, with the Thielert lagging a bit at low altitude and outdistancing the Lycoming higher up. I suspect that a 172 or Warrior with a constant-speed prop would handily outclimb both its fixed-pitch counterpart and the Thielert-engined version at low altitude, because it would be able to make full use of its 160 horsepower at all speeds.
Propeller pitch corresponds to transmission gear ratio in a road vehicle. It's true that an engine with greater low-end torque, like a big truck’s diesel, will be better able to keep up revolutions, and therefore power output, at low rotational speed. In road terms, we would say that it will not "lug" or "bog down" in the way a less torquey engine might if it were not provided with a sufficiently low gearing. A constant-speed prop is analogous to a continuously variable transmission, adjusting engine speed to provide the desired horsepower at all times. A car or truck with such a transmission, or with a sufficiently wide range of closely-spaced gears, would climb a hill rapidly even if it lacked low-end torque, because it would be able to keep its engine speed, and therefore its power output, high. It is not true that, given suitable transmissions, of two vehicles of equal horsepower the one with the higher torque will climb better. Climb is all about horsepower, not torque; in fact, the very definition of horsepower is based on the rate at which a weight can be raised.
With regard to fixed-pitch props, a "climb" prop is one that has sufficiently flat ("fine") pitch to allow the engine to develop high rpm at climbing speed. A "cruise" prop is coarsely pitched, to preclude its over-revving at cruising speed. Racing airplanes have props pitched for top speed, but they take off sluggishly; glider tugs have climb props and can’t get up much steam for cruise. Normal passenger-carrying airplanes have compromise props that don’t allow the engine to achieve full power during climb, and require that it be throttled back during cruise.
With regard to the TwinStar, one may wonder how a four-seat twin is going to achieve a positive climb rate on a single 135-hp engine. Presumably the folks at Diamond have worked out the answer. It can only be that superior aerodynamic efficiency, particularly in the form of a large wingspan, reduces the power required for climb. Merely to lift 3,000 pounds at, say, 250 fpm requires 23 horsepower, which translates into something closer to 30 when prop losses are taken into account. Airframe and cooling drag at 90 knots will probably require another 80 hp, which translates, again, into 100 or so from the engine.
The Thielert diesels come into their own in cruise. They have a genuine FADEC, or Full Authority Digital Engine Control—a single lever that electronically manages both fuel flow and rpm. Because the efficiency of an internal combustion engine improves as its compression ratio increases, diesels naturally burn less fuel per horsepower-hour than gasoline engines do. They also run on jet fuel, which currently happens to be 10 to 20 percent cheaper, on average, than avgas, or on road diesel fuel, which is cheaper still. Maximum power may be used at any time; the conventional limit of 75 percent for cruise does not apply. Being turbocharged, the diesel is essentially flat-rated over the range of altitudes that a 172 or Warrior would most often use, and so is faster than they are at high altitude. Throttled back to economy cruise, it achieves unusually long range—provided that the pilot has the Sitzfleisch to match.
It is not surprising that certified aviation diesels have appeared in Europe. The cost of fuel there is much higher than it is here, and so the prospect of significantly reduced direct operating costs softens the blow of the Thielert engines' price, which is higher than that of present gasoline-burning types. That they should be expensive is not surprising; they are complex, sophisticated machines in comparison with the rather simple ones they aim to replace.
Those Pesky V-speeds
Several readers pounced on my statement that maneuvering speed drops with weight, pointing out that a just-short-of-stalling pull-up at the gross-weight maneuvering speed produces the same air loads on the wing regardless of the airplane weight, even though the occupants may experience a higher G force. True enough. But the wing spar is not the only structural component in the airplane. Many others are designed to support fixed loads. The engine mount, for example, is designed to support the engine at a certain load factor, and the higher acceleration experienced by a lighter airplane during a pull-up to a stall at the gross-weight maneuvering speed could exceed that factor.
One hawk-eyed observer, Dick Reilly, pointed out that my statement that all of the characteristic speeds of an airplane, including best rate and angle of climb speeds, are functions of angle of attack, does not hold true in practice for airplanes with fixed-pitch propellers. I would like to say that I had omitted to mention this caveat in the interest of keeping things clear, but actually I just never thought about it. Since the efficiency of the fixed-pitch prop depends on true rather than indicated airspeed, the indicated speeds for best rate and angle of climb are lower, at high altitude, than the appropriate angle of attack for those conditions would imply.
That may sound clear, but try and remember it the next time you're dragging a 172 over a saddle in building cu at 14,000 feet.
Diesel Engines May Make a Comeback as Planemakers Seek Alternative Fuels
At least four firms are developing diesel engines for non-turbine, high-performance light aircraft that will run on Jet A1, thereby freeing operators from dependency upon leaded high-octane avgas that is headed toward extinction early in the 21st century. The new diesels promise one-third better specific fuel consumption than current leaded gas piston engines.
Morane Renault Engines' 200-hp, five-liter, four-stroke, four-cylinder MR 200 turbo-diesel made its U.S. debut at EAA AirVenture '98 (the Oshkosh show). It made its first flight on an Aerospatiale Socata TB20 in March.
Meanwhile Lycoming, together with partner Detroit Diesel, is developing a turbo-diesel engine. And Continental is pressing ahead with a 4.7-liter, two-stroke, 4-cylinder CSD-283 engine as part of the NASA-GAP (General Aviation Propulsion) program. The Morane Renault MR 200, including accessories, weighs 13 pounds less than a 200-hp, four-cylinder, Lycoming piston engine, according to Luc Pelon, the company's program manager. Turbocharging and the large intercooler enable the engine to develop 70 percent power at 25,000 feet. The engine has a digital electronic control and power is set with a single lever.
The MR 200 features an 18:1 compression ratio, plus head-to-head through bolts that allow use of very high boost pressures. Similar to slow turning diesel engines used in trucks, the MR 200 generates its 200 hp at a comparatively slow, constant 2,000 rpm. It uses high boost, instead of high rpm to generate its rated power and make possible a 3,000-hour TBO, according to Pelon. External noise levels should drop five to six dB because of low prop rpm plus the muffling effect of the turbocharger, said Pelon.
JAA Part 23 certification is slated for third quarter 1999. FAA certification is expected shortly thereafter. The turbo-diesels will make their production debut aboard Socata general aviation singles.
Morane Renault also is developing 250- and 300-hp versions of the four-cylinder turbo-diesel. Both engines have 3:2 reduction gearing, thereby allowing the prop to turn 2,000 rpm while the engine turns at 3,000 rpm. The MR 250 and MR 300 also are scheduled for certification in 1999 and they weigh considerably less than gasoline-fueled, six-cylinder engines that produce equivalent horsepower. Installed cost is projected to be about 10% more compared to engines that burn avgas. For example, retrofitting an MR 300 might cost $60,000 to $90,000. Life cycle costs, however, should be lower because of increased maintenance intervals.
In contrast to Morane Renault's MR 200, Lycoming-Detroit Diesel's four-stroke, four-cylinder engine weighs 20% more than its current 200-hp, four-cylinder gasoline powered IO-360. The TDIO-360 has a 16:1 compression ratio, it runs at a maximum 2,400 rpm and maximum boost is limited to 60 inches MAP. The engine has a conventional hydro-mechanical fuel control. Preliminary tests of the TDIO-360 proof-of-concept engine are complete.
The next step is a 500-hour endurance test in preparation for fourth quarter 1999 certification. Lycoming hopes to pare 10 to 15% of the excess weight from the engine by certification. Continental is pressing ahead with a 4.7-liter, two-stroke, four-cylinder CSD-283 engine as part of the NASA-GAP (General Aviation Propulsion) program. By Fred George

Last edited by klhansen; 06-10-2008 at 12:30 PM. Reason: Fixed link and removed a bit of the gasoline related stuff so it fit within the word count limit!!
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Old 08-22-2005, 07:12 PM   #10 (permalink)
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Re: Jet A vs Diesel

Holy crap batman!!!!
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Old 08-23-2005, 02:33 AM   #11 (permalink)
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Re: Jet A vs Diesel

WEll I'm going to throw down some of my own experiences with Jet A.
I do maintenance activities for a major airline and
we at least twice a month have to defuel ERJ-135, ERJ-145, XRJ-145 aircraft (same size as the G-IVSP or G5). We had a guy that would fill his F350 with Jet A on Lunch break once a week for years. He put over 80,000 miles on Jet A and had no problems with anything,,,,well he had a bigroblem when Airport Police saw what he was doing and that led to him being fired.

Also our GPU's always run on Jet-A and they say on the side to either put Jet-A or Diesel in them. So With all this I don't see Jet A hurting a diesel, even more so if it's only for a couple hundred gallons worth.

Oh yeah I remember him always saying that he got crappy mileage when the fuel had a ton of prist in it. Said it was like winter blend.




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Old 06-10-2008, 09:35 AM   #12 (permalink)
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Very interesting topic, thought I would bring this thread back up. Hmmm funny when I logged in it was telling me I last visited on 12-31-1969...

Anyway even though this board is more for big rigs does anybody have an idea what the use of Jet-A would do to a stock '84 VW 1.6 Diesel engine?

Thanks for your input.

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Old 06-10-2008, 02:01 PM   #13 (permalink)
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In no way should you use it in your x. With that being said I would be willing to take it off your hands Really, we ran bio-diesel in some support equipment and it cost big dollars to fix the problems. We now run exclusively JP8-100. These engines have never run so good.
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Old 06-10-2008, 03:42 PM   #14 (permalink)
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did ya actually read all this? i did!

Quote:
Originally Posted by Blitzkrieg View Post
I contacted Marketing Fuel Technical Service at Chevron
and asked my question. What I received back was a BOOK and here it is:

"In regards to your inquiry about whether Jet A can be run in a diesel engine, Chevron would never advise anyone to use a particular fuel in an engine that was not designed for that fuel. We would advise that the inquiry be made to the equipment (engine) manufacturer."

Remember, while there is only one basic Jet A species, there are several kinds of diesel - diesel No. 1 and diesel No. 2 (amongst others). Jet A is more like Diesel No. 1. Diesel No. 2 is the more common "diesel" fuel, since it is the fuel used by vehicles "on-road".

All of the fuels are products of the refining process. One of the main differences between them is their distillation boiling ranges. Diesel No. 2 has a higher (in temperature) boiling range and is more dense than Jet A and/or diesel No. 1 (both of which have lower densities and lower boiling range temperatures). A fuel which is less dense will have lower fuel economy (less BTU's per gallon). All of this is "besides the point" as far as the appropriateness of any of the three to perform in the engines that were designed for their use. If the engine manufacturer indicates the use of only one type of fuel, that is the fuel that should be used.

For further information please visit Chevron's INTERNET site at Chevron Corporation Home Page
There are some very informative publications at the site at http://www.chevron.com/chevron_root/prodserv (there is an "underscore" character after the second "chevron" word). When you reach that site, click on the word "Fuels" and you will then see a "Publications" option.

That said, we will break down your inquiries into a group of statements that we have put together to answer others who have asked similar questions:

Jet A, Diesel No. 1, and Diesel No. 2, are covered by different American Society For Testing and Materials (ASTM) specifications. The diesel fuels are covered by ASTM D 975, "Standard Specification for Diesel Fuel Oils". Jet A has the designation of ASTM D 1655, "Standard Specification for Aviation Turbine Fuels".

According to the ASTM specifications listed above, the sulfur limit for Jet A is a maximum of 0.3 mass %. Because of an Environmental Protection Agency 1993 regulation, the specification for sulfur in "on road" Diesel No. 1 and Diesel No. 2 is a maximum of 0.05 mass % - a large difference from the Jet A sulfur level.

The EPA regulation would be broken if one were to use Jet A for "on-road" Diesel. Jet A is also not taxed for "on-road" use, so would be illegal to use in "on-road" vehicles and possibly illegal in some "off-road" uses as well. Both the sulfur level and the tax issue need to be considered in a legal sense when considering the uses of these fuels.

Another difference between the fuels is the viscosity. The ASTM D 1655 detailed viscosity requirement of Jet A is a maximum of 8 mm2/S (millimeter squared/Seconds - [1mm2/S = 1 Centistoke]) at -200C. The ASTM D 975 viscosity requirement of Diesel No. 1 is a minimum of 1.3 and a maximum of 2.4 mm2/S at 400C and of Diesel No. 2, a minimum of 1.9 and a maximum of 4.1 mm2/S at 400C. It is hard to compare these, since the testing temperatures of the diesels do not agree with that of the Jet A. However, the viscosities at 200 Centigrade and in units "milliPascal/Seconds" (still another, and different unit measurement) for the two fuels according to a national average of four semiannual surveys taken from 1990-1992 are as follows:

Jet A & Diesel No. 1 1.33
Diesel No. 2 3.20

Jet A and Diesel No. 1 tend towards lower viscosities. Lower lubricity is likely as the viscosity decreases. While this may not cause catastrophic instant damage, it could cause long-term wear of pumps, etc.

Jet fuels have additional specifications that aren't required of diesel fuels. A couple examples of these are the requirement of testing for certain components and a volatility requirement. Some of the methods for testing also vary from one fuel to the other. Basically, however, we have pointed out the biggest differences. If you need more detailed comparisons, please contact the ASTM society at their headquarters at 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428. They could provide you with copies of the specifications. Their phone number is 610-832-9500.

Once again, we stress that you should contact the equipment manufacturers and ask what fuels are proper for use in the engines you are curious about. Also, you must make certain you are not breaking any legal regulations."

So the bottom line is that although Jet-A may not cause immediate damage to a diesel engine and may allow the engine to run OK, its use may cause premature wear or fouling of the fuel system, and you may be breaking EPA regulations as well as not paying appropriate taxes. Outside the US, differences in viscosity still mean that the use of Jet-A for Diesel No. 1
may cause early wear of the fuel system. Kind of like running 10 weight oil in a car designed for 30 weight. So how much risk are you willing to take, because no engine manufacturer or fuel supplier will take part of the risk?


Diesel vs Jet Fuel
A New Diesel Fuel Additive Requirement
ASTM D-975, the ASTM standard for diesel fuel, is being modified to include a specification on diesel fuel lubricity. Lubricity is the fuel quality that prevents or minimizes wear in diesel fuel injection equipment. Diesel lubricity is largely provided by trace levels of naturally occurring polar compounds which form a protective layer on metal surfaces. Refinery hydrotreating processes which reduce the sulfur content of diesel blend components also remove these polar compounds. As a result, most of the diesels produced by refineries to meet January 1, 2006 ultra-low sulfur diesel (ULSD) sulfur specifications will not have adequate lubricating properties to meet the new ASTM lubricity specification.
Baker Petrolite is a leading provider of diesel lubricity improvers, fuel additives that restore the lubricating properties of severely hydrotreated diesel fuels. These additives have traditionally been added at the refineries producing the fuels.

In 2004 some major U.S. finished fuel common carrier pipeline companies announced that they would not allow the transport of diesel fuels already treated with lubricity improvers. This is due to their concerns about “trail back” of the lubricity additive into jet fuel tenders following the additized diesel, which are not allowed to contain these additives. As a result, most lubricity additive usage in the U.S. will take place at fuel terminals.
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WHAT ABOUT FUELS?
There are six things to consider when comparing hydrocarbon fuels:
1. Volatility. In short, what's the fuel's propensity to vaporize. This effects the ability to easily mix the fuel with air and the fuel's tendency to vapor-lock. It also determines the pollution characteristics of the fuel where evaporative pollution is a concern.
2. Pre-ignition & knock resistance. Referred to as "Octane value." How much energy does it take to get the fuel burning - how much does it resist auto-ignition from compressive heat? Also, what is the rate of burn of the fuel (which affects the rate of pressure rise)?
3. Energy content. How much energy can be extracted from the fuel as a percentage of its volume or mass.
4. Heat of evaporation.
5. Chemical stability, neutrality, and cleanliness. What additives does the fuel contain to retard gum formation? Prevent icing? Prevent corrosion? Reduce deposits?
6. Safety
The first three factors are often confused and interrelated when, in fact, they measure three completely separate things. There is no natural collelation between them.
General rules:
Heavy fuels (diesel, jet): Low volatility, low knock resistance, high energy per volume
Light fuels (gasoline): High volatility, high knock resistance, low energy per volume
Note that gasoline, partially, makes up for its (relatively) low energy-per gallon by the fact that a gallon of gasoline weighs less (by about 15%) than a gallon of jet fuel.

HOW DOES THE OCTANE OF DIESEL AND/OR JET FUEL COMPARE TO GASOLINE?
Diesel and Jet fuel (along with kerosene) have, indeed, terrible octane numbers; typically about 15-25 "octane". They tend to ignite easily from high compression. Their use in a gasoline engine will quickly destroy the engine.
Diesel fuel is rated by its cetane number which is determined, like octane, by running the fuel in a test engine. Instead of heptane and iso-octane they use napthalene (cetane rating = 0) and n-cetane (cetane rating = 100). In total opposite to octane ratings, the higher the cetane rating the higher the fuel's propensity to knock!
Just as using a fuel with an octane number higher than necessary in a gas engine will gain you noting, using a fuel with a cetane number higher than necessary in a diesel engine gets you nothing. On the other hand, where using a fuel with too low an octane number in a gas engine will result in a damaged engine, using a fuel with too low a cetane number of a diesel engine will just result in a rough-running (or not running at all) engine with no damage.
WHAT'S THE DEAL WITH DIESELS?
Why can diesel engines tolerate a low octane fuel? In all gasoline engines, (including injected gasoline engines!) the fuel/air mixture is present in the cylinder the entire time the piston is travelling upward on its compression stroke. This means it could be ignited at any time whereas we only want it to be ignited when the spark plug fires, some time just before the very top of the stroke. Furthermore, we want a nice, even, steady, pressure rise in the cylinder as a result of ignition. This means that we want the flame-front to travel linearly from the source of ignition (the sparkplug) to the other side. We do not want combustion to occur randomly within the mixure as that may cause a too-rapid pressure rise which will throw off all our calculations about where the piston should be and when.
First, In a diesel engine there is NO fuel in the combustion chamber as the piston starts up on its compression stroke. Instead, fuel is injected at high pressure (up to 3000PSI!) into the combustion chamber at the exact moment when ignition is desired. In a diesel engine with a compression ratio of around 20:1 (compared to 7:1 for many modern gas engines), the heat of compression will have raised the combustion chamber temperature to arond 1000-1500F. The injection time takes about .002-.004 seconds during which the fuel spontanously ignites from the heat of compression at just the right time. Even so, a diesel fuel with too low a cetane rating may not ignite, or may ignite poorly - especially on cold days starting a cold engine.
The second critical difference is that Diesels are set up to burn the fuel in a slightly different way.
In a gas engine, you typically set it up so that the mixture is ignited before the piston hits the top of the stroke. What you're aiming for is for the mixture to be fully burned around the top of the stroke - thus combustion pressures are maximized at the top of the stroke and gradually fall off as the piston moves downward on the power stroke (and increases the volume in the cylinder). Diesels, on the other hand, are set up to inject fuel very close to the top of the compression stroke. The fuel spontenously ignites (auto-ignition) and, actually, knocks just like it does in does in a gasoline engine (hence the classic diesel "knocking"). The combustion pressures in the diesel increase evenly as the piston goes down. The net result is that the diesel piston "feels" a constant pressure on it as the piston travels from top dead center to bottom dead center whereas a normally operating gasoline engine piston "feels" a constantly decreasing pressure as it travels to the bottom of the stroke. The net result is that the diesel feels a lot lower PEAK pressure while the pressure is maintained over a longer period. The gasoline engine feels a much higher peak pressure which starts to fall off immediately as the piston travels downward. The implication, for the latter, is that it periodically operates very close to the capabilities of the base metals. Anything, such as knocking, which increases those peak pressures even more is apt to push beyond the capabilities of the base metals and result in engine damage.
Knock in a gasoline engine tends to occur at the end of combustion, when pressures inside the cylinder have reached, as a result of spark ignition, very high values - values high enough to auto-ignite the fuel.
Knock in a diesel engine happens at the beginning of combustion as a direct result of piston compression only. It is what allows further combustion as the piston moves downward. This continued combustion keeps the cylinder pressure constant as the piston moves towards BDC.
WHAT DOES A HIGH OCTANE VALUE MEAN, TO ME?
A high octane rating ensures that it takes a REALLY hot ignition source to ignite the fuel (such as a spark plug or the flame-front itself) and not just the rise in pressure & temperature that's a result of normal combustion. Note that the thermal rises in the cylinder are in direct proportion to the compression ratio of the engine (more below). The higher the compression ratio, the higher the octane of the fuel that's needed.
Again, if the mixture in a gasoline engine ignites before the spark plug fires, we call that "pre-ignition." Pre-ignition can damage an engine before you finish reading this sentence. To reiterate, what we're really concerned with is called "knock" and that's the spontaneous ignition of the fuel-air mixure ahead of the flame-front as a result of the rise in cylinder pressure caused by the onset of ignition (caused by the firing of the spark plug).
WHAT ABOUT AIRCRAFT?
Now, back to aircraft. We want to make aircraft engines with the following characteristics:
1. Very high power/weight ratio
2. Low specific fuel consumption (so we don't need to carry around heavy fuel)
The easiest way to do this, without involving lots of complex machinery that might fail and add weight, is to raise the compression ratio of the engine. An engine's efficiency is in direct proportion to its compression ratio. Unfortunately, raising the compression ratio means we need to protect against knock/detonation. How do we do this? We use high (100 octane) fuel!
Driving Fuelishly BY JAY LENO, Published on: April 16, 2002
Alternative, renewable and old--all attributes that keep Leno partial to his 1909 Baker Electric and its well-made, long-lasting batteries
People ask me what I think of cars that use alternative fuels. Naturally, I have an opinion. I had a chance to drive the new BMW 750hL dual-fuel hydrogen car. It uses some existing technology: an internal-combustion engine and conventional automatic transmission. But it also has two separate gas tanks, and a button on the dash that you press to switch the engine from gas to hydrogen power. BMW built its own hydrogen-filling station in Oxnard, Calif., which is kind of critical--the infrastructure for hydrogen fuel doesn't exist. Hydrogen isn't hard to make, though. In California, there are units out in the desert that convert sunlight into hydrogen. It's not perpetual motion yet, but it's truly a renewable source you will never run out of. And what comes out of the tailpipe is water that's pure enough to drink. You convert that to hydrogen and you use it again. That's pretty neat.
As far as electric cars go, the technology isn't really new. I have a 1909 Baker Electric that goes 110 miles on a single charge. A General Motors EV-1 goes maybe 120 miles. So in nearly 100 years we've only come 10 extra miles. You can take the Baker's Edison batteries, wash 'em out and use 'em again. They're beautiful-looking even though they're almost a century old.
Here's the problem I have with modern electric cars. Talk to tow truck operators and see if they'll tow one. When an electric car gets into an accident, you've got more than the usual problems, what with 300 volts running through it. Are they gonna want to tow this thing with busted wires? Let's say it catches fire. What's the fire department gonna do? I wonder what the AAA manual says?
Personally, I think the best alternative fuel is one we already have, but this country doesn't want to produce: No. 1 refined diesel fuel. Diesels are 30 percent more fuel-efficient than spark-ignition engines. And a gallon of diesel has 10 percent more energy than a gallon of gas. You go to Europe and you can get a VW Golf that gets something like 60 mpg. You could bring that over here and it would sell just fine. It runs best on ultralow sulfur content No. 1 diesel, which burns cleanly and is very similar to jet fuel. For some reason, we don't want to produce high-quality, commercially available desulphured diesel fuel in this country, though some experts say we will by 2006. Meanwhile, our diesel fuel is filthy. When I run aviation fuel in my jet motorcycle it burns clean. But if I use regular diesel, it chokes the people behind me to death.
As for hybrids like the Honda Insight and Toyota Prius, I think they have wonderful technology. For someone like me who likes to drive, the Honda is fine. I enjoy it. I mean, if I'm in a performance car, I want to get as much performance out of it as I can. But in an economy car, I want to drive with my socks on. You know, touch the pedals lightly and see how much economy I can get. Either way, I enjoy playing the game. But the VW turbodiesel does everything the Honda Insight does--maybe even better. The European model gets better mileage, but it's not sexy. It doesn't have that sleek little shape with the fender skirts. It doesn't look like the future.
Obviously, the last days of an old technology are always better than the first days of the new. The final steam cars, like the Doble, which would get a head of steam up in less than half a minute, were better than the first gas ones. Eventually, we'll get there.
How Do Thielert Diesels Do It?
By Peter Garrison
October 2004
One reader castigated me for not paying enough attention to Thielert diesels. Another inquired whether the just-certified Diamond TwinStar would have superior climb performance because of the great torque of its Thielert diesel engines. A critical mass of Thielert interest has evidently been reached.
Thielert GmbH is located at the small town of Lichtenstein in the former East Germany (not to be confused with the principality of Liechtenstein, wedged almost invisibly between Switzerland and Austria). The company produces, among other things, liquid-cooled geared turbo-diesel aircraft engines based on Mercedes automotive designs. A 1.7-liter, 135-hp four-cylinder is currently certified for retrofit to Cessna 172s and Piper Warriors originally equipped with the 160-hp Lycoming O-320 engine. The Austrian firm of Diamond offers its single-engine Diamond Star with one of the engines, and the upcoming TwinStar has two. More than a hundred Thielert-powered airplanes are now flying, and the company expects to certify a 4.0-liter, 310-hp V-8 this year.
It's unusual to offer an engine of lower power to replace one of higher. One wonders where the company gets the chutzpah to do it. The answer is that, at least in the 172 and the Warrior, performance is barely affected, gaining a little in some areas and losing a little in others. To understand how this can be so when the new engine is apparently much weaker than the old, we need to look at the characteristics of diesel and gasoline engines.
To start with, their combustion cycles are fundamentally different. The gasoline engine draws a fuel-air mixture into the cylinder, compresses it, and finally ignites it with a spark. The need to avoid spontaneous ignition (either pre-ignition or detonation) limits the compression ratio, while the need to ignite and burn the compressed mixture requires that the ratio of fuel to air remain within fairly narrow limits. An air throttle, linked to a fuel valve in injected engines, regulates power, while a mixture control allows fine adjustment of fuel flow in order to ensure a combustible, but not wasteful, fuel-air ratio.
The Thielert engines have no air throttle. Only engine speed regulates the amount of air they take in, while fuel flow controls their power output. Rather than a fuel-air mixture, only air is compressed by the rising piston. A very high compression ratio—18:1, more than double that of a typical unsupercharged aircraft gasoline engine—raises the temperature of the air in the cylinder (because the same amount of heat energy gets crammed into a much smaller volume of air) above the point at which hydrocarbon fuels ignite spontaneously. No timed spark is needed; fuel, sprayed into the cylinder under extremely high pressure as the piston reaches the top of its travel, burns regardless of the fuel-air ratio, which is always, by gasoline-engine standards, very lean. There is no harm, after all, in having excess air being present, just so long as there is enough oxygen to react with all of the hydrocarbons in the fuel. Jet engines, too, take in far more air than they use for combustion.
In their familiar roles as powerplants for generators, trucks and ships, diesel engines are typically designed to be slow-turning but to have a long stroke. The stroke, which is the distance the piston travels, is twice the crankshaft’s "throw"; the throw, in turn, is the maximum length of the lever arm against which the piston exerts its pressure. Long throws ensure that diesels yield plentiful torque. Since horsepower is the product of torque and engine speed, a slow-turning engine with lots of torque can work as hard (that is, produce the same horsepower) as a faster-turning engine with lower torque. Torque is naturally determined not by crank geometry alone, however, but also by the pressure in the cylinder during the power stroke and by the area of the piston (which is as much as to say the "bore" of the engine).
Although the 135-hp Thielert Centurion 1.7's weight, around 300 pounds, is similar to that of the 160-hp Lycoming O-320, its displacement is less than a third of the Lycoming's. It achieves its maximum power at 2300 prop rpm—3900 crank rpm—versus 2700 for the Lycoming.
While it is tempting to suppose that the key to the similarity in takeoff and climb performance between the Lycoming- and Thielert-powered versions of the 172 and the Warrior lies in the diesel's superior torque, in fact both engines deliver about the same torque—around 300 pound-feet—to the propeller. I suspect that the explanation is really more mundane. The Thielert engine uses an automatic variable-pitch propeller, whereas the Lycoming, in these airplanes, drives a fixed-pitch prop. During takeoff and climb, the Lycoming does not achieve maximum rpm, whereas the Thielert does. The superior aerodynamic efficiency of the Thielert's propeller nearly erases whatever residual power advantage the Lycoming might have, and so the takeoff distance and rates of climb for the two engine types turn out to be quite similar, with the Thielert lagging a bit at low altitude and outdistancing the Lycoming higher up. I suspect that a 172 or Warrior with a constant-speed prop would handily outclimb both its fixed-pitch counterpart and the Thielert-engined version at low altitude, because it would be able to make full use of its 160 horsepower at all speeds.
Propeller pitch corresponds to transmission gear ratio in a road vehicle. It's true that an engine with greater low-end torque, like a big truck’s diesel, will be better able to keep up revolutions, and therefore power output, at low rotational speed. In road terms, we would say that it will not "lug" or "bog down" in the way a less torquey engine might if it were not provided with a sufficiently low gearing. A constant-speed prop is analogous to a continuously variable transmission, adjusting engine speed to provide the desired horsepower at all times. A car or truck with such a transmission, or with a sufficiently wide range of closely-spaced gears, would climb a hill rapidly even if it lacked low-end torque, because it would be able to keep its engine speed, and therefore its power output, high. It is not true that, given suitable transmissions, of two vehicles of equal horsepower the one with the higher torque will climb better. Climb is all about horsepower, not torque; in fact, the very definition of horsepower is based on the rate at which a weight can be raised.
With regard to fixed-pitch props, a "climb" prop is one that has sufficiently flat ("fine") pitch to allow the engine to develop high rpm at climbing speed. A "cruise" prop is coarsely pitched, to preclude its over-revving at cruising speed. Racing airplanes have props pitched for top speed, but they take off sluggishly; glider tugs have climb props and can’t get up much steam for cruise. Normal passenger-carrying airplanes have compromise props that don’t allow the engine to achieve full power during climb, and require that it be throttled back during cruise.
With regard to the TwinStar, one may wonder how a four-seat twin is going to achieve a positive climb rate on a single 135-hp engine. Presumably the folks at Diamond have worked out the answer. It can only be that superior aerodynamic efficiency, particularly in the form of a large wingspan, reduces the power required for climb. Merely to lift 3,000 pounds at, say, 250 fpm requires 23 horsepower, which translates into something closer to 30 when prop losses are taken into account. Airframe and cooling drag at 90 knots will probably require another 80 hp, which translates, again, into 100 or so from the engine.
The Thielert diesels come into their own in cruise. They have a genuine FADEC, or Full Authority Digital Engine Control—a single lever that electronically manages both fuel flow and rpm. Because the efficiency of an internal combustion engine improves as its compression ratio increases, diesels naturally burn less fuel per horsepower-hour than gasoline engines do. They also run on jet fuel, which currently happens to be 10 to 20 percent cheaper, on average, than avgas, or on road diesel fuel, which is cheaper still. Maximum power may be used at any time; the conventional limit of 75 percent for cruise does not apply. Being turbocharged, the diesel is essentially flat-rated over the range of altitudes that a 172 or Warrior would most often use, and so is faster than they are at high altitude. Throttled back to economy cruise, it achieves unusually long range—provided that the pilot has the Sitzfleisch to match.
It is not surprising that certified aviation diesels have appeared in Europe. The cost of fuel there is much higher than it is here, and so the prospect of significantly reduced direct operating costs softens the blow of the Thielert engines' price, which is higher than that of present gasoline-burning types. That they should be expensive is not surprising; they are complex, sophisticated machines in comparison with the rather simple ones they aim to replace.
Those Pesky V-speeds
Several readers pounced on my statement that maneuvering speed drops with weight, pointing out that a just-short-of-stalling pull-up at the gross-weight maneuvering speed produces the same air loads on the wing regardless of the airplane weight, even though the occupants may experience a higher G force. True enough. But the wing spar is not the only structural component in the airplane. Many others are designed to support fixed loads. The engine mount, for example, is designed to support the engine at a certain load factor, and the higher acceleration experienced by a lighter airplane during a pull-up to a stall at the gross-weight maneuvering speed could exceed that factor.
One hawk-eyed observer, Dick Reilly, pointed out that my statement that all of the characteristic speeds of an airplane, including best rate and angle of climb speeds, are functions of angle of attack, does not hold true in practice for airplanes with fixed-pitch propellers. I would like to say that I had omitted to mention this caveat in the interest of keeping things clear, but actually I just never thought about it. Since the efficiency of the fixed-pitch prop depends on true rather than indicated airspeed, the indicated speeds for best rate and angle of climb are lower, at high altitude, than the appropriate angle of attack for those conditions would imply.
That may sound clear, but try and remember it the next time you're dragging a 172 over a saddle in building cu at 14,000 feet.
Diesel Engines May Make a Comeback as Planemakers Seek Alternative Fuels
At least four firms are developing diesel engines for non-turbine, high-performance light aircraft that will run on Jet A1, thereby freeing operators from dependency upon leaded high-octane avgas that is headed toward extinction early in the 21st century. The new diesels promise one-third better specific fuel consumption than current leaded gas piston engines.
Morane Renault Engines' 200-hp, five-liter, four-stroke, four-cylinder MR 200 turbo-diesel made its U.S. debut at EAA AirVenture '98 (the Oshkosh show). It made its first flight on an Aerospatiale Socata TB20 in March.
Meanwhile Lycoming, together with partner Detroit Diesel, is developing a turbo-diesel engine. And Continental is pressing ahead with a 4.7-liter, two-stroke, 4-cylinder CSD-283 engine as part of the NASA-GAP (General Aviation Propulsion) program. The Morane Renault MR 200, including accessories, weighs 13 pounds less than a 200-hp, four-cylinder, Lycoming piston engine, according to Luc Pelon, the company's program manager. Turbocharging and the large intercooler enable the engine to develop 70 percent power at 25,000 feet. The engine has a digital electronic control and power is set with a single lever.
The MR 200 features an 18:1 compression ratio, plus head-to-head through bolts that allow use of very high boost pressures. Similar to slow turning diesel engines used in trucks, the MR 200 generates its 200 hp at a comparatively slow, constant 2,000 rpm. It uses high boost, instead of high rpm to generate its rated power and make possible a 3,000-hour TBO, according to Pelon. External noise levels should drop five to six dB because of low prop rpm plus the muffling effect of the turbocharger, said Pelon.
JAA Part 23 certification is slated for third quarter 1999. FAA certification is expected shortly thereafter. The turbo-diesels will make their production debut aboard Socata general aviation singles.
Morane Renault also is developing 250- and 300-hp versions of the four-cylinder turbo-diesel. Both engines have 3:2 reduction gearing, thereby allowing the prop to turn 2,000 rpm while the engine turns at 3,000 rpm. The MR 250 and MR 300 also are scheduled for certification in 1999 and they weigh considerably less than gasoline-fueled, six-cylinder engines that produce equivalent horsepower. Installed cost is projected to be about 10% more compared to engines that burn avgas. For example, retrofitting an MR 300 might cost $60,000 to $90,000. Life cycle costs, however, should be lower because of increased maintenance intervals.
In contrast to Morane Renault's MR 200, Lycoming-Detroit Diesel's four-stroke, four-cylinder engine weighs 20% more than its current 200-hp, four-cylinder gasoline powered IO-360. The TDIO-360 has a 16:1 compression ratio, it runs at a maximum 2,400 rpm and maximum boost is limited to 60 inches MAP. The engine has a conventional hydro-mechanical fuel control. Preliminary tests of the TDIO-360 proof-of-concept engine are complete.
The next step is a 500-hour endurance test in preparation for fourth quarter 1999 certification. Lycoming hopes to pare 10 to 15% of the excess weight from the engine by certification. Continental is pressing ahead with a 4.7-liter, two-stroke, four-cylinder CSD-283 engine as part of the NASA-GAP (General Aviation Propulsion) program. By Fred George
My comment:

According to the ASTM specifications listed above, the sulfur limit for Jet A is a maximum of 0.3 mass %. Because of an Environmental Protection Agency 1993 regulation, the specification for sulfur in "on road" Diesel No. 1 and Diesel No. 2 is a maximum of 0.05 mass % - a large difference from the Jet A sulfur level.

Avjet-A is .0005 sulphur to as high as .0015 sulphur. Ultra low ULSd is i think 15 parts pe million?

I would have no problem running avjet-A in a pre DPF engine with a little standyne for lubrication but in any 2008 DPF engine you will have a problem.
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Old 02-24-2009, 11:27 AM   #15 (permalink)
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Jet-A will not cause major problems quickly! I know a man that used sump fuel in his VW Jetta and saved enough money to buy his wife a CAR! He had hundresds of thousands of miles on that car and carries 3 5Gal. jugs to fill with sump fuel (with permission) to fuel his car. Fill-er-up and mash on it! I would recommend some mystery oil (I have used this since 14 in airplanes and cars and big trucks, works good) to clean and lube on occasion.
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