Why can?t a Diesel engine be designed to run on gasoline?
I?m not saying to run gasoline in any old Diesel.
Why not design a Diesel compression principle engine with injectors and fuel pump designed to handle gasoline, with high enough compression to guarantee combustion, with injector timing and duration to maintain combustion throughout the power stroke, etc. We all know gas engines love to diesel sometimes.
I?ve never heard a good explanation why this would not work, except for maybe lower power output, but what the hey, its gas.
For that matter, why wouldn?t the diesel principle work for any fuel? Jet fuel, kerosene, even alcohol?
The compression on a diesel engine is already WAY higher than a gasoline engine. If what you suggest were possible, such a vehicle would need TWO gas tanks, TWO fuel infection systems, etc. It all adds up to too much complexity, which is only ONE of the reasons why your idea won’t work.
Gasoline engines don’t “love to diesel.” They only do it when there is something wrong with them.
Keep dreaming, John. Some day maybe you’ll come up with a theory that has merit.
I need a scientific argument why this won?t work. Like say, the high octane buffers in modern gasoline, which are there precisely to prevent preignition, would prevent the fuel from igniting under compression only (no spark). But then higher compression would overcome that and also lend to better burn efficiency.
Dieseling in old carbureted engines happened due to (among other things) hot carbon built up in the engine from crappy burning. Couldn’t shut the fuel off as with injection.
“Scientific argument?” I’m not a scientist. BUT; Where will you put the second fuel tank? How will you engineer the second fuel injection system? Is this even possible?
If this were feasible, it would already be done. Do you think you are the first person to think of this?
Please don’t say, “Yes.”
Before I make a complete fool of myself, isn’t Mercedes Benz working on something along these lines? An engine that works on spark ignition part of the time and compression ignition part of the time.
I’ve read reports that they are working on such an engine.
John, maybe you should go to work for Mercedes Benz. You are a genius!
Why would you want to?
Yes, but Mercedes is not the only one.
GM currently has a working prototype of a Saturn Aura
But, there are certain times when these engine NEED a spark to completely ignite the fuel and provide good power and emissions. In particular, at very light loads and at very high loads. Also, at very low rpm and very high rpm.
Under most driving conditions it operates without any spark.
10%-15% increase in fuel efficiency with the same power output.
You might investigate the “multi-fuel” engine of the 1960s 6x6, 2.5 ton military trucks.
Wow, this is actually a good question, but a good answer may take up a lot of space. I hope I can do this.
Flame propagation is the simple answer. Once ignited, the flame spreads at a set rate. Some of the factors that affect this is the fuel itself, the fuel air ratio and the size of the fuel droplets in the mixture. The fuel droplets are fairly consistent with in a volume of fuel/air mixture, not that all droplets are the same size, but that there is the about the same ratio of small, medium and large droplets within each volume measured. That means that the flame will spread at about the same speed on each power stroke.
Diesel engines ignite on compression, so ignition timing occurs at about the same point on each stroke regardless of engine speed. As the engine builds up speed, the pistons reach a point where they “outrun” the flame. At this point, power drops off fast, that is why diesels have such a narrow power band. Gas engines on the other hand use an ignition system where the timing can be adjusted to compensate for engine speed and fuel air ratio. This allows them a much larger power band. If you have ever had the weights stick on the mechanical advance of an old distributor, you will know how much that affects the power band.
Then there is the issue that diesel fuel is combustible while gasoline is flammable. That means that the ignition temperature of gasoline is at or below room temperature while diesel fuel has an ignition temperature well above room temperature. That makes trying to use the diesel principle on a gas engine at lot more hazardous and harder to control.
BTW diesel fuel and JP-5 jet fuel are both a form of kerosene. JP-4 and Jet-A have some gasoline added to increase the jet engines efficiency, but it makes it flammable. Many aviation safety specialists want the airlines to use JP-5 or add an anti-misting compound to Jet-A to reduce the chances of fire during a crash. I guess thats to keep the body’s from burning and making it easier to identify them. Surviving a 100+ mph impact with the ground is not likely, fire or no fire.
Engineers can do a great number of things; running a diesel on gasline will work with only one fuel on board, but he result would be a less efficient diesel than if you ran it on diesel fuel, because of the lower heat content. The best gasoline engine would use direct gasoline injection, very high compression ratio (12+:1 or so)and variable valve timing to get high output with good efficiency. But it could not equal the best diesel engine, with or without turbo-charging.
In Europe, more than half of new car sales are diesels, for fuel efficiency reasons. If a gas powered diesel was more efficient, that’s what they would be using. Unfortunately Europe now has an unbalanced refinery load, and experts its excess gasoline producred to the US.
I’m not sure why you posted the question, perhaps out of curiosity. If all the engines in the world were diesels, refineries would be simpler, and we would have that pesky, explosive by-product called gasoline to contend with. Making the high proportionof gasoloine out of crude oil, as is needed in the US, requires expensive “cracking” and other equipment.
It’s already been done. In the 40s International used a combo for starting their big engines. We had several TD14 and TD18 crawlers with about 700 CC engines that started on gas thru a large compression release valve that opened into another combustion chamber with valves, plugs in all cylinders. This started the engine on gas and after warmup, the Valve is closed and diesel fuel enters thru injectors. Some of those tractors are still in use today. LEE
Good explanation, the difference is the combustion characteristics of these fuels. In a gasoline engine, the combustion is essentially instantaneous, taking place near TDC. The resulting pressure pushes the piston through the power stroke (the pressure reduces as the piston moves down). In a diesel engine, the combustion speed is much slower, similar to the piston speed at the most efficient engine speed. In this case, the combustion starts near (actually before TDC) but continues throughout the power stroke. As a result, the pressure is (more or less) constant throughout the power stroke. The combustion speed is what limits the engine speed in a diesel. We are talking about two completely different thermodynamic cycles, each of which requires specific fuel characteristics. It’s my understanding that the proposed “gasoline powered” diesel cycles will require very sophisticated fuel management systems.
I think the OP was asking for a CI engine that will run on gasoline instead of #2 fuel oil (diesel fuel). No spark ignition or compression relief as in the TD14/18. As has been asked before, what’s the point? Refining to diesel is more energy efficient than refining to gasoline, and gasoline may well burn too fast (compared to oil) to deliver a smooth power cycle. By the way, wasn’t the original design by Rudolph Diesel intended to run on coal dust?
Mr Phil, you’re right on Dr Diesel designing the engine to run on coal dust or corn cobs or any number of things that could be pulverived. but the dyno juice was easiest and most plentiful with little preparation. LEE
Some high performance engines of the 1960s ran at near self-ignition compression ratios of 11 to 1. It’s possible to make a diesel cycle gasoline powered engine, running at a compression ratio of about 12 to 1; but, I don’t think it would be efficient or reliable.
Since gasoline has a narrow range between self-combustion and detonation, it would be difficult to prevent detonation. A flame front travels much faster in gasoline than in diesel fuel. With diesel fuel, there is, likely, a 1 or 2 degrees of crankshaft rotation difference in compression self-ignition each time combustion happens. In a gasoline diesel-cycle engine, the time of self-ignition could be several degrees of crankshaft rotation. Since the flame front travels much faster in gasoline, there would be a shorter, but greater pressure, impulse on the piston, and cylinder walls, and cylinder head.
An actual gasoline diesel cycle engine would be an interesting “feasibility study”, if anyone would build one.
There is an undelying economic/technical rationale as well. A barrel of crude is GENERALLY refined into high octane aviation gas (avgas), gasoline, diesel, jet fuel, heating oil, and residual oil. What is left is ashphalt, and other bottoms. Some refineries extract lube oil as well. In North America we need a lot of gasoline, an average amount of diesel, some heating oil (becoming less so),a and below average amount of residual oil. US refineries traditionally got this from light crude oils and used catalytic cracking and other processes to more gasoline for all those cars.
Europe traditionally produced a more balanced mixture because of small cars, shorter distances driven and relatively more diesels.
At this time, crudes are getting heavier on average and US refienries can’t produce the right mix of products. New refineries are under construction to produce more gasoline from heavy and synthetic crudes as well as produce ultra low sulfur diesel (ULSD) for the new wave of diesels hitting the market soon.
To make best use of crude oil, we need both diesels and gas powered vehicles. But industry would not use gas engines since they are inherently less efficient, mostly due to the limits on cormpression ratio, as explained before. It just does not pay to try to make a gas engine as efficient as a diesel, as pinted out by others.
The high level of automotive diesels in Europe is partly due to a preferential price sytem; in Italy, diesel costs about 2/3 as much as gasoline.
Let me illustrate some of my thinking that I left out of my original post for the sake of brevity. I aint no engineer so forgive me here. The biggest gasoline combustion problem is detonation because of the hammering and cutting torch effect on the piston. GM came up with the ?Wedge Head? design to smooth out the combustion impulse across the entire piston.
With a spark ignition, all the fuel is there waiting for immediate ignition. In a Diesel, the fuel is introduced gradually. No fuel is in the cylinder before it needs to be so no preignition. With direct injection, the fuel is introduce gradually and would alleviate detonation/preignition problems since the mechanical injectors simply cannot work that fast. For that same reason there could never be a 10,000RPM Diesel. Yes the gasoline fueled Diesel would have a limited RPM range and more gears would be necessary.
With a gasoline Diesel, there would be no need for octane additives, MTBE etc. and therefore would make refining much easier.
You can?t take a barrel of oil and refine it into just Diesel fuel. There will be some gasoline resulting from the process and as long as we?re living with crude, we?ll have to deal with gasoline.
Certainly modern engine computers could adjust injector timing, rate of spray & other parameters I can?t even think of. For an outrageously complicated combustion computational problem, try googling ?HCCI Combustion?. If they can do that, this should be a piece of cake.
At one time there was a concept called stratified charge (for spark ignition). If I remember right, at TDC the charge was rich in the center near the spark plug (hemi) and leaner towards the outsides. I think it was a swirling charge idea (keep that thought). It must have been tough to do, I?m not sure anyone ever went into production with it. The ideas was that the mixture was just rich enough at the spark to get the flame started and was lean burn through the rest of the power stroke (cooler flame).
Honda had a good idea with a head design where the charge was lean but there was a small combustion chamber off the main chamber, with its own intake valve and the spark plug. I think it was called an antichamber or something like that. The fuel charge that came into this chamber was rich enough to spark the flame front, which then spread to the main chamber. That doesn?t have anything to do with this conversation but I thought it was an interesting concept.
OK, back to the original point. If a gasoline fueled Diesel had enough compression, lets say 20:1 or more, plenty hot enough to guarantee ignition, and a lean but long duration injector spray so that there is no hammer effect on the piston, what could possible go wrong? I could see the injector getting carboned up from crappy burning. That could be an issue. If the injector was pointing directly at the piston it could behave like a cutting torch on the piston but a ceramic coating on the piston head could take care of that.
Lets go bake to the swirling charge idea. Lets consider this engine is a 2-stroke. I thought I was genius for dreaming up a 2-stroke Diesel but GM has apparently has had them for a half century in locomotives. Anyway, lets introduce supercharged air into the cylinder in a swirling fashion and instead of pointing the injector straight at the piston, mount it near the edge of the chamber at an angle into the swirl, so that it sprays as if into a spinning turbine. Now the combustion takes place as a flow more than just an explosion. Also, how about a full time glow plug to guarantee ignition. With a full time glow plug, the compression could be reduced and the spray mixture could be leaned even more.
How about a Wankel Diesel? OK, save that for another thread.
On a separate note, be sure to google ?Biodiesel Production from Algae? from the University of New Hampshire Physics Department. It?s a fascinating read.
Is this the kind of design you are talking about?
Thats it! THANKS! I think you’ve got it. The “DiesOtto Engine”. It says “Some, like direct injection, already are seen on a variety of engines from numerous manufacturers.” That must mean conventional Diesels. Otherwise I’ld like to hear about these numerous manufacturers.