Gas engine to diesel conversion idea
Friday August 03, 2007
Fuel injected gasoline engines cannot burn diesel fuel because of several reasons.
GASOLINE ENGINE Computer injected, spark ignited, Low torque: total ignition at or before TDC
DIESEL ENGINE Mechanical direct injection, Compression ignition, High torque: Prolonged diesel ignition during powerstroke
Solution to conversion
1)Injection system: Diesel injection pump, 2)Ignition system: Injection line heating to above autoignition, 3)High Torque: Modify injection pump to reduce injection duration at all speeds
Ok, so how can we do this?
Replace spark plugs with diesel injectors, and remove gasoline fuel injectors. Install pulley driven diesel fuel injection pump on the engine and connect fuel lines to the injectors.
So, the fuel will be delivered to each cylinder at TDC as the pump rotates.
How to ignite it?
Heat each injector line to above autoignition temperature with an electric cable heater wrapped around it. This allows cold, low compression air to ignite with fuel already at autoignition temperature. High compression air is not needed.
Now that you are setup how can you make the system create less torque so you don't destroy that gasoline engine block?
Gasoline engines cannot handle the torque levels of a diesel, they wear out very quickly. The source of diesel torque is not the fuel, but the prolonged injection of diesel throughout the power stroke.
Modify a diesel injection pump to a short injection pulse while at slow speed. This normally only happens when the pump is at high speed. If the fuel is injected very quickly rather than in an extended injection down the power stroke, torque will drop. All the while maintaining precise timing of injection and power of the engine.
You could just use a bigger injection pump pulley, but timing of injection will be off.
You're done! Since you figured out how to modify that injection pump smarty pants.
Now some possible feasibility conditions:
1) heated fuel results in coked(clogged) injector 2) Injector loses lubricity and wears out due to loss of viscosity due to fuel heating 3) Fuel line connection failure due to heat 4) Injection duration is not short enough at low throttle on injection pump which results in engine damaging torque-- danheathmoore, Aug 04 2007 Diesel Engines and Public Health http://www.ucsusa.o...-public-health.htmlDiesel is a major polluter and carcinogen. Cheaper isn't always better. [Ander, Aug 04 2007] Oh I forgot, diesel injectors will have to be modified to fit and seal the spark plug hole. And the gas pump in the tank will have to swapped out, maybe the whole tank.-- danheathmoore, Aug 04 2007 Erm, why would you want to do it? (I can think of some reasons, but it would be good to hear yours)
A few (of the suspected many) issues.....
The exhaust system. The gearbox (different RPM for same power output). Probably lots of electronics in any modern car.
Basically, the short cut is sell your car and buy a diesel car.
By the way, it _is_ quite easy to modify petrol cars to run on LPG, if anyone's interested. This is actually done in various European countries.-- AllyAl, Aug 04 2007 WHY? Double the fuel mileage of course. Oh, and I could run biodiesel, veggie oil(with a kit) waste veggie oil, straight veggie oil.
Also, I need to modify not only the injection pulse but the maximum speed governor in the pump too to allow original gasoline engine RPM range.-- danheathmoore, Aug 04 2007 BIG PROBLEM: There would probably be no air fuel swirl to mix in the igntion delay before TDC because of piston head design.
If the fuel is vaporizing shortly after injection because of extreme pre-injection fuel heating. Some mix would occur because of vapor and air dynamics.
Also, the drop in temperature of the fuel due to expansion from injection, colder air in cylinder may require very high temperatures in injection line.
Just my extra thoughts.-- danheathmoore, Aug 04 2007 Automakers have tried to adapt gasoline engines for diesel use. The results have generally been quite poor. Diesel engines have to operate at higher compression ratios than gasoline engines; unless a gasoline engine is excessively over-engineered, the extra stresses would almost certainly lead to premature failure.-- supercat, Aug 04 2007 Pay attention. No high compression needed, no high torque generated. Same RPM range of power created.-- danheathmoore, Aug 05 2007 When I was young my brother put diesel fuel into the tank of petrol engine moped. It ran but turning off the ignition did not turn off the motor but the engine kept running and only way to stop it was to drive slowly against a wall and stall the engine that way, lol.-- Pellepeloton, Aug 05 2007 //Pay attention. No high compression needed, no high torque generated. Same RPM range of power created.//
We are paying attention. This is pure conjecture on your part and you offer absolutely no information to validate these comments. No references, no prior art, no reasonable inferences, No nothing. Just your opinion. You don't even provide the temperature at which Diesel fuel is shown to auto ignite. If it were as easy as you imply someone would have done it, the fact is no-one has done it so you need to cough up some real info here and cut the attitude.
The operational requirements of a deisel cycle engine are radically different from those of a gasoline engine. The designs of both have been optimized to a very high degree. What they share is really a superficial design layout and appearance and that is about it otherwise they are really totally different machines that are really not cross compatible.
Bottom line while what you propose may be POSSIBLE with enough screwing around you will find that all the changes needed to make it work will result in an engine that doesn't exhibit any of the benefits of the a comparably sized diesel engine. Odds are it will actually be less efficient than either its true gasoline or diesel counterparts while being more polluting than both.-- jhomrighaus, Aug 05 2007 What [jhomrighaus] said.-- normzone, Aug 05 2007 I understand your position. I am not looking for same fuel efficency or pollution.
I am looking for an economical way to convert over to biodiesel, wvo, svo without the cost of a new engine swap. Labor cost involved.
This could be a kit custom designed for the gasoline engine to be converted. Now, I would like ideas on how to increase swirl, fuel mixing in ignition delay...to improve efficiency and pollution.
Forget references, I don't care about that, I'm discussing the mechanics of an idea.
If you've got a problem with these facts, tell me which one is wrong. I'd really appreciate that.
By the way, supercat was the one not paying attention. So chill.-- danheathmoore, Aug 05 2007 [danheathmoore], please see the help file over there on the left, under "meta".
And there's not enough compression in your gas engine to ignite the diesel.-- normzone, Aug 06 2007 Your whole premise is entirely incorrect and this idea has no chance of achieving its goal. That is my position.-- jhomrighaus, Aug 06 2007 The same as a scout starts a campfire by way of a bow, a few sticks and friction, a slap-together kit might work from sheer simplicity. Forget momentarily that engineering would make the task efficient by refinement and reduce all those nasty pressure imbalances and hot spots.
I'm going out to convert my old walk-behind lawnmower to diesel -- sounds like more fun than mowing grass.-- reensure, Aug 06 2007 I'm not nearly convinced about the heated - fuel - in - lieu - of - compression idea, but I'll give you the benefit of the doubt. I do wish to correct some of [supercat]'s misconceptions, however. Petrol-based diesel engines are in fact quite frequently and thoroughly baked. Some of the most successful smaller automotive diesels out there have been developed from SI engines. The Volkswagen EA827 springs to mind. The first diesel version of that engine appeared in the mid '70's, and millions of them have given very impressive service over the past thirty years. That engine is well suited to a diesel version because it has a strong bottom end to begin with and, having been designed to fit lengthwise in the short nose of the first Audi 80, it has a tight bore spacing and has consequently always tended to undersquare cylinder dimensions in its various versions. Similar engines have been made by Mercedes-Benz, Peugeot, and others.
So, provided you've got a longish-stroke engine with a solid bottom end, it's no impossibility. You will, however, need to go to a compression ratio in the order of 17-22:1. Torque output will be slightly LESS than with spark ignition, but the power and torque peaks will occur at lower engine speeds. Expect about 35bhp/litre at 3500-4000rpm for a naturally-aspirated, non-electronic diesel.-- Ned_Ludd, Aug 06 2007 Correct me if I am wrong but the "conversions" you have described all involved a complete re-engineering of the Cylinder head, the entire intake system, the front engine cover, the valve train and of course a new transmission.
What you have described is radically different than just pulling out the spark plugs, bolting on a fuel pump and swapping the computer. You are describing a re-engineered engine(not unlike the B series engines in MG's and Morris's that originated as a tractor engine)-- jhomrighaus, Aug 06 2007 FWIW, my dad had a gasoline-engined car that couldn't be shut off. It just kept chuffing and clonking away, not very happily, until it cooled down some and finally quit. He said it was 'dieseling'.-- baconbrain, Aug 06 2007 tis pre-ignition and is known as dieseling cause that is what is happening. The gasoline mixture is igniting due to heat and compression in the chamber. This cant really happen in a modern car as the flow of fuel stops when the injectors stop but was possible on a carburetter engine.
This is most often caused by carbon buildup in the engine. A cup of water slowly poured into the carburettor usually takes car of it.-- jhomrighaus, Aug 06 2007 I wish I'd known that cure back then. Thank you.-- baconbrain, Aug 06 2007 ps. you pour the water in very slowly with the engine running. Slowly enough so that it does not stall out. These days the best stuff Ive found for this is called Seafoam and its sold in a red can at most parts stores.-- jhomrighaus, Aug 06 2007 in carby is anti diesel solenoid valve (creative name huh?) to prevent fuel flowing after ignition is turned off. (fuel in carby at float level will be drawn off by venturies and will in most cases cause a warm engine to "diesel" for a short time if anti diesel solenoid is stuck open).-- the dog's breakfast, Aug 07 2007 Ah, I love the smell of bio-diesel fuels because it reminds me of eating greasy food! We should seriously consider converting to edible fuels just because we should be able to cook a few hamburgers and hotdogs in our engine while we drive to work in the morning. I like the yin and the yang of alcohol and greasy foods burning in our engines! I wonder if there is also a way to make efficient tobacco oil engines and gunpowder engines too.
Well, this is not a very emperical approach like I would try to take, but then again, neither was Henry Ford's approach either. There's just something about your idea that says "I have access to a machine shop and I have plenty of money to do trial and error tests in order to make one of my gas-to-deisel engine conversion attempts eventually work" This is the Thomas Edison approach to doing stuff that Henry Ford learned while working at the Edison Electric Company back in the old days.-- quantum_flux, Sep 02 2007 So the two reasons for this conversion are:
1: fuel efficency 2: use of biofuels
well in order to get this to work you would need to:
Replace spark plugs with diesel injectors and modify fuel system.
Replace the engine computer
raise the compression ratio with a turbocharger.
It would probably work, but i doubt it would be very efficent, especially if using your idea of preheating the fuel. Diesels get most of their efficency from their high compression ratios, the rest from the higher energy density of the fuel. It would also be expensive, the engine would wear prematurely due to the high compression, and I'm sure the EPA wouldn't let you do it.
The only other justification would be the ability to use biodiesel. It would be much cheaper and easier to convert a gasoline car to run on ethanol, just a matter of changing the computer, fuel sensor and coating the aluminum intake ports with some sort of epoxy or something since ethanol tends to dissolve aluminum.
But the best thing to do would be for us all to use Butanol. Its a 4-carbon alcohol which is interchangeable with gasoline. I can be made by fermentation like ethanol.
http://www.butanol.com/-- Livingfishguy, Sep 03 2007 a little off track..
I never heard of Butanol as a fuel. Looks better than any of the alternatives but you still have to be able to produce it somehow without useing more energy than the product can produce.-- F_R_O_G, Sep 03 2007 I'm convinced that the cheapest way to get a diesel, in order to run on vegetable oil, is to sell your current vehicle and buy an old diesel-powered VW.
/Gasoline engines cannot handle the torque levels of a diesel, they wear out very quickly. The source of diesel torque is not the fuel, but the prolonged injection of diesel throughout the power stroke./
I've never seen that "fact" before, but true or not, it's not the real problem. The detonation that ignites the fuel in a diesel is extremely violent. When it occurs in a petrol engine, it can cause severe damage in a short time.
Yes, modern cars base their petrol and diesel engines on one block that is strong enough for either. The same can't be said for the heads though, and I'm not sure about pistons either.
The costs involved in making this work would vastly outweigh the benefits. If it's straight veg oil you're after, it's an old-tech diesel you need - newer designs tend to have their sensors totalled by it IIRC. The cars these are in are worthless; you wouldn't be able to convert your petrol engine for that price.-- david_scothern, Sep 04 2007 Since his purpose is just to run bio-diesel, in a gasoline engine, couldn't he do what the army did to run coal in a diesel: REALLY lean out the gas and then mist in diesel in the intake. His compression isn't high enough to ignite the diesel, but when the gasoline ignites off the spark, it will then light the diesel. PS the diesel VW engines of the 70s were very little like the gas versions as the blocks also had to be resigned to handle the pressure and the cranks were also stronger. That is why they put a 1.5 liter diesel in the space of a 1.7 liter gas. PS I still miss my old VW diesel pickup, except the paint job, lime green.-- MisterQED, Oct 29 2007 random, halfbakery