Converting a petrol engine to run on diesel

Hawk Tuah

Hawk Tuah

Hawk Tuah

Soldato
Joined
18 Oct 2002
Posts
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Location
Sandwich, Kent
Right, before you start with the bunsen burners, I have no intention of trying this. Its merely hyperthetical. Suppose you have a fully laden machine shop. The knowlege of how to use all the tools, the time, money and inclination to do it.

What would it take to make a petrol engine run using diesel fuel. Now my knowlege of petrol engines is a lot better than diesels.

To start off, technically a diesel and a petrol engine are the same. They all have cylinders, pistons and rods and a crank shaft, cams, injectors, intake and exhaust valves.

So if you were going to do it, you would need.

Different injectors?
Something to warm the fuel?
Different air fuel ratios?
Different ignition timing and components (glow plugs?)
 
Erm, a lot of work i reckon!

First off, you would have to change the spark plugs for glow plugs, also, dont diseasal engines need a lot more compression??
 
Compression and strength of the internals must be higher in a derv?

And even with all the tools in the world the head / ports can't be the same you need an add more metal tool.
 
Normally a deisel engine is a lot stronger as its running much higher compression so assuming the petrol block was strong enough you would need to beef up the internal componants. You would need injectors, a deisel pump, glow plugs for starting then the head would have to modified to take the extra parts(assuming thats strong enough). Compression ratio of the engine also needs to be increases by either skimming the head or with different internals.
 
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Bug One said:
I take it those two are linked then.

Why, whats different?
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Derv engine doesn't work like a petrol in terms of a spark ignites the fuel, in a derv unit the compression action does, hence the higher internal strength.

The head / cams / timing on a petrol engine can't be the same as a derv one, no spark plugs so those holes would need to be blocked up, location of the glow plugs on the derv block might not be the same as the spark plugs, derv unit doesn't regulate the fuel by changing the flow to the injectors it does it all at the pump, also i don't think a derv has a throttle body?

Not to mention all the sensors ecu fuel pressure in the lines / tank etc
 
Bug One said:
Right, before you start with the bunsen burners, I have no intention of trying this. Its merely hyperthetical. Suppose you have a fully laden machine shop. The knowlege of how to use all the tools, the time, money and inclination to do it.

What would it take to make a petrol engine run using diesel fuel. Now my knowlege of petrol engines is a lot better than diesels.

To start off, technically a diesel and a petrol engine are the same. They all have cylinders, pistons and rods and a crank shaft, cams, injectors, intake and exhaust valves.

So if you were going to do it, you would need.

Different injectors?
Something to warm the fuel?
Different air fuel ratios?
Different ignition timing and components (glow plugs?)
Click to expand...
Different ignition timing? There are no spark plugs in a derv. :p As long as your valves are timed correctly, you are good to go. Also derv don't have a fixed air fuel ratio either...

Didn't the early mark 2 golfs use a very similar (1.5? 1.6?) petrol and diesel engine? I think they used bits of the petrol engine and made it run on diesel, but it was slow as hell...
 
So, in diesel, the air fuel mixture enters the cylinder and they ignite via the glow plug at a certain compression level, right at the apex of the pistons movement? Why not use a spark like in a petrol engine?

Is a diesel more efficient because the air fuel can be compressed more, and hence a more potent reaction is possible? If so, why dont they compress petrol more, or would that cause premature detonation?
 
Bug One said:
So, in diesel, the air fuel mixture enters the cylinder and they ignite via the glow plug at a certain compression level, right at the apex of the pistons movement?
Click to expand...

The glow plug is just to help the engine block/cylinder heat up. It's the heat generated by compression that ignites the fuel-air mixture.
 
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As said, the diesel block is stronger than the petrol one due to it running on compression not spark, so you may blow apart the petrol block...would be interesting to see that happen, if it would. :p

As for the glow plugs, they are only used to get heat in to start the engine, once started, they are not used again...from what I understand anyway.

InvG
 
InvaderGIR said:
As said, the diesel block is stronger than the petrol one due to it running on compression not spark, so you may blow apart the petrol block...would be interesting to see that happen, if it would. :p

As for the glow plugs, they are only used to get heat in to start the engine, once started, they are not used again...from what I understand anyway.

InvG
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Yep, I had a glow plug go, and my engine had problems starting and even then it would run rough for a few minutes as it wasn't warmed up properly... Once it's warm, the glow plugs are not needed.
 
Bug One said:
So, in diesel, the air fuel mixture enters the cylinder and they ignite via the glow plug at a certain compression level, right at the apex of the pistons movement? Why not use a spark like in a petrol engine?
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No, the fundamental difference between petrol and diesel engines is that only air enters the cylinder via the inlet valve. The fuel in injected directly into the combustion chamber when the piston nears TDC, and immediately starts to combust due to the high temperature of the air. The ignition timing is purely down to when fuel is injected. Because ignition doesn't rely on a tiny concentrated heat source (i.e. a spark) the mixture can be run very lean and still burn ok. This is why diesels operate without throttles (or at least used to, some modern ones have throttles to help reduce Nox emsissions).

The old 2-stroke model compression ignition engines used of RC planes etc. worked more like a petrol as they had a carburettor and an air/fuel mix entered the cylinder. However, the point at which the mixture ignited was very loosely controlled and could only be determined by adjusting the compression ratio. They also didn't use diesel!

Converting a petrol engine would be pretty much a non-starter unless the petrol happened to be derived from a diesel in the first place. A diesel engine has far heavier, stronger internal components, completely different piston and cylinder head designs and you would need to find some way of injecting the diesel with accurate timing.
 
InvaderGIR said:
:(

Replace them first then...I just want a 'I blew my engine up...literally' thread/photos. :p

InvG
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Thats easy.

big_turbo.jpg


Clarkson style :p
 
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