Is it technically feasible to convert *the same* engine from diesel to petrol or vice versa?
ie. with the major components still in situ? The same engine block, pistons, con rods etc. albeit extensive mods to fuel system.
Before you laugh yourselfs silly this is a serious question, Now i know it's not practical and costs would be prohibitive but is it possible?
Reason i ask is i was moaning to SWMBO about cost of petrol lately and she said why can't you convert it to diesel? (D'OH!!)
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I'm sure the teckies could word it better, but the answer is surely a big No. They are fundamentally a different construction, compression ratio being just for starters (factor of around 2 difference).
Oz (as was)
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Ignoring turbines (as I guess was intended), and concentrating on reciprocating (piston) engines, some in a relatively low state of tune have been designed to run on pretty well "anything" that ignites.
Petrol, diesel, parafin, avgas, and so on.
A number of battle tank engines have been thus designed, because reducing reliance on one fuel type increases the ability to fight if the supply chain is affected.
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Reckon a DI diesel engine could be converted to run on petrol if an ignition system could be fitted, if the injectors could be replaced by spark plugs, if a carburetor and suitable manifold could be fitted or indirect injection achieved into the existing manifold and if the compression ration could be lowered by taking a chunk off the top of each piston, pointless exercise though because it would be too much of a compromise
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Sorry, I should have said, yes a silly question!
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Even if you could get the engine to handle the compression needed for a diesel you'd need to replace the pistons/conrods/bearings in the bottom of the engine to handle the extra work per revolution. But the block, with the spark plug holes blanked off, might be useable. Not much else.
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...with the spark plug holes *on the head* blanked off... Er, no, you can't do it.
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Diesels is thicker than petrol. There may be issues in getting it through a petrol injection system?
OK the other way, but what do you ignite the petrol with?
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Diesels is thicker than petrol. There may be issues in getting it through a petrol injection system?
Petrol injection requires a fuel which will vapourise in the inlet manifold/carburettor venturi. Diesel will not vapourise (easily). Therefore the diesel would just trickle past the valves and not go with much of a bang at all.
OK the other way, but what do you ignite the petrol with?
I suppose you could insert a matrix material somewhere into the combustion chamber which would store heat in a not so dissimilar method to coking the engine would do. Then theoretically it should self-ignite under this heat and compression. Don't know what you'd do about cold starts though?
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Mike Farrow
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Orrrrrrrr.......
....you could just buy a diesel/petrol car.
Crazy I know.
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Adam
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Its not as silly as it sounds. A lot of diesel engines are based on major petrol engine components. Blocks, bottom ends, crankshafts etc.
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perkins 236 on the american market was either petrol or diesel but the same basic engine for both fuels with carb/distributer /plugs or injectors/pump fitted.
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>>A lot of diesel engines are based on major petrol engine components. Blocks, bottom ends, crankshafts etc.
Based yes.components need to be able to cope with high stress levels at low revs.so a diesel cannot be compared to petrol..If anyone needs to convert to diesel they should buy a diesel engine/convert fuel system. though on most it wont be cost efficient.unless its an old motor.even then I would forget it
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Steve
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Its not as silly as it sounds. A lot of diesel engines are based on major petrol engine components. Blocks, bottom ends, crankshafts etc.
Weren't the 1.4 Peugeot XUD Diesel engines based on petrol engines?
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A few years ago our local bus operator ran a 'clean, green' Bristol VRT double-decker that was converted to run on Liquified Natural Gas. From what I remember reading the engine was based on the normal Gardner 6-cylinder diesel but fitted with spark plugs insted of injectors and presumably a gas/air mixing device to produce a mixture to be drawn into the cylinders. I'd guess the compression ratio had to be lowered too.
Cheers, Sofa Spud
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Lots of CHP (generator sets) run on natural gas using similarly converted diesel engines, Caterpillar, MAN, etc..
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As said, it's the higher compression ration for diesels that would be the killer - the forces on the conrods and crankshaft would destroy petrol engined components in a very short time.
The answer is that anything's possible, but the only componenets you'd probably carry over would be the alternator!
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Here's a tidbit to nibble on.
'kits' were available during the war (ww2) to lower the CR of an engine. this enabled cars to run on the awful fuel available at the time. I believe it was called pool petrol, and was about 67 octane. the kit consisted of a machined plate that you put betweenthe head and block, something very easy to do with a side valve motor. this would help going diesel to petrol, and I suppose you could get away with it on the valves. (cambelt would have enough slack for the few millimetres it would take, but it would throw the valve timing out a bit. You could probably adjust an OHV motor ok, if not then its a simple job machining a longer set of pushrods.
Going petrol to diesel presents another problem. Short of skimming the head or block or both, I think the only other options are higher compression pistons or a new crank with a larger 'throw'.
something else:old 2 1/4 land rover petrol/diesel engines are basically the same engine. but the crank was either cast or forged, depending on petrol or diesel. just to make it interesting, not only were they physically interchangeable, they both had the same part number! so ordering a crank for a diesel could be a lottery, with a good chance of hitting the jackpot!
WTM
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