I know because it’s not designed for it, but what actually stops it from working. You have a fuel sprayed into a high pressure/temp environment and all it seems to have to do is ignite. The compression seems high enough to autoignite gas, as that happens at a lower pressure then diesel. What makes this not work, and what, if any, modifications can be made to allow use of gas as a fuel in a diesel cycle?
High temp environment doesn’t exist in a diesel engine, only high pressure. Well, once the diesel is burning, the high temps exist, but there is no spark. Diesel/air is compressed and ignites in a diesel engine under great pressure and the timing is very controllable, where as gas/air is compressed AND ignited via a spark/plug to effect the timing. Diesel can be compressed significantly and the combustion isn’t going to happen so early that power is lost. You get gobs of power from really compressing it.
The gas/air mix requires an ignition source/system to properly control the timing. It’s a dance to keep compression set right and prevent pre-combustion and let the spark advance time the ignition to fire the piston downward at just the right moment.
So, what stops gasoline from working in a diesel engine is chemistry and/or physical laws based on the elements and compounds we are working with.
So could gas be used in a preheated diesel engine? Gasoline cars sometimes run on after the ignition is turned off in a process called dieseling, so a spark is not required.
Your post already states that gas can and does ignite under compression without a spark (pre-combustion), so it is possible.
The problem is predetonation. That knocking you hear is gas igniting and damaging the engine. Will gas burn? Sure. Will the engine run? No. To make the engine run, the gas/fuel needs to detonate at the right time. Not much value when the detonation happens while the piston is on the way up.
So, two issues must be distinguished from each other: W*ill gasoline burn in a diesel engine? *versus will gasoline work in a diesel engine?
Your title post is about it working, and why not. It won’t work because it (gas/air) must be properly compressed (not overly compressed) and the proper timing must be effected by the spark. Will it ignite/burn? Sure. You need more than that for power.
Not much value when the gas/air blows up while the piston is on its way up.
Caveat: We are talking about a typical production diesel engine, and understanding why gas won’t make it run.
I want to hear from some of the dopers who have operated a tank in the military. A buddy of mine did, and I thought for sure he told me that those engines were built so that they could run on just about any type of fuel imaginable.
Gasoline at that level of compression explodes, rather than burn as it does in a gasoline engine; it doesn’t combust at the intended / predicted point of piston travel but instead goes off when the air-fuel mixture is squeezed tightly enough for gas to ignite of its own accord, probably while the piston is still moving forward to compress it some more. Essentially you’d damage the engine without getting much useful energy from the gasoline.
It’s sort of like using lye instead of baking soda to get rid of your indigestion: yes, it is another alkaline substance and yet it will neutralize acids in your stomach, but no, that’s not a good idea.
Addressing this: those engines were built so that they could run on just about any type of fuel imaginable
Then they are NOT diesel engines. They would go by a different moniker.
See my caveat.
Those tanks use a turbine as a power plant. Since a turbine doesn’t use a fixed thermodynamic cycle, there’s more flexibility in the fuel which can be used. Pretty much anything that burns can be used in a turbine… natural gas, gasoline, diesel, paraffin wax… Though, of course, a given turbine will be designed to give optimal performance with a particular fuel.
Diesel engines can be designed so that they have a bit more flexibility in fuel choice. Kerosene and jet fuel are slightly lighter fractions that diesel, but they can be used in properly-designed diesel engine. Gasoline is still far too volatile to work effectively in a diesel cycle, however.
To elaborate a little:
From here: “Gasoline is formulated to resist auto-ignition in a spark engine (see octane), so this fuel introduced into a diesel engine either won’t ignite or will (much more likely) ignite at the wrong time causing severe detonation. Though diesel engine reciprocating components (pistons, wrist pins and connecting rods) are built to withstand enormous explosive force, the shock wave effects of uncontrolled detonation can easily destroy them.”
From here: “Should you discover that gasoline has been introduced into your diesel fuel tank, do not so much as even start your engine. Gasoline can create so much heat in the fuel system that injectors can melt.”
The Master speaks: “What happens when you use gasoline in a diesel engine? Either something expensive or something very expensive. Since gasoline is designed to be resistant to self-ignition, gasoline in a diesel engine either won’t ignite or will ignite at the wrong time. Some diesel engines run leaner than gasoline engines (meaning that the air-fuel mix has a higher proportion of air than a gasoline engine). That increases the chances that the gasoline won’t ignite and that unburnt fuel will be sent into the hot exhaust system–where, ironically, it could ignite, leading to possible exhaust damage.”
So sometimes, depending on the particular engine and the particular gasoline, it won’t run because of incompatibly between the fuel formulation and the ignition process (high compression). In other cases, it will run briefly before causing significant damage, after which it won’t run because of said damage.
Nitpick: It’s “Mistress.”
An oversight on my part, and my apologies.
OTOH, what would happen if you introduced Diesel fuel into a gasoline-powered engine?
Maybe, but there’s plenty of military vehicles that are conventional diesel-cycle piston engines that are designed to run on anything from kerosene to gasoline to diesel to jet fuel. See for example: M35 series 2½-ton 6×6 cargo truck - Wikipedia
I believe a lot of the earlier Cold War era tanks used a similar arangement where there was a diesel engine that was designed to run on most anything. These multi-fuel engines have at least been around long enough that every now and again I see them come up for sale on craigslist.
It does also bring up one other major issue with using gasoline in a diesel engine, though-- diesel acts as a lubricant and usually fuel components on diesel engines (notably the injector pump) will rapidly wear out if run with gasoline. But the engines that are designed to run on gasoline do so just fine, increased wear notwithstanding.
From the same column by Una that Gary T linked to:
The only thing I can add from personal experience is that diesel fuel will not work in a Ford Pinto.
Gasoline engines diesel when carbon deposits are hot enough to act as an ignition source.
A gas engine is a spark ignition engine.
A fuel/air mixture enters the cylinder. The piston compresses the mixture. At the proper timing a spark ignites the mixture.
A diesel engine is a compression ignition engine. Air enters the cylinder. The piston compresses the air, the compression of the air increases the temperature. At the proper timming diesel fuel in injected into the cylinder. The high temperature ignites the fuel as it enters the cylinder. Depending on the throttle setting will determine the injection time.
As GreasyJack said,
" It does also bring up one other major issue with using gasoline in a diesel engine, though-- diesel acts as a lubricant and usually fuel components on diesel engines (notably the injector pump) will rapidly wear out if run with gasoline. But the engines that are designed to run on gasoline do so just fine, increased wear notwithstanding. "
Also the viscosity gas and diesel are different. The spray pattern from the injector with gas would be wrong, the droplets would be large causing explosions
rather than a burn. That is if the pin in the injector would lift fully and cleanly, I think they would dribble and open and close but not cleanly. Also because of the short burn times I think the peak temperatures would be high causing overheating in a short time. Plus the unburned fuel going out the exhaust would cause problems.