Anti knock additives for diesel engines

I'm curious, how does a change of ECU tweak help? I thought, perhaps incorrectly, the ignition in diesel engines was due to compression only (therefore piston position).

Isn't that how diesel engines work anyway? High compression rates until the mixture self-ignite.

Injection timing is quite critical. The fuel is supposed to burn as its injected into the hot compressed air.

If it's early the compression won't have increased cylinder air temp to ignition point. Then you have a lot of fuel in the cylinder just waiting for the air temp to rise which is delayed by the fuel cooling it. Kaboom!

If it's late the peak cylinder pressure will be reduced and there may be fire out of the exhaust ports.

Either way power is reduced.

That makes more sense but I thought the fuel air mix was compressed, not the air and the fuel added. It seems I was wrong.

Thank you.

Add some AVgas to the fuel.

That used to be the case but direct injection changed things so that the air is compressed and then the fuel is injected to be ignited as it goes in.

A homogeneous charge engine that induces and air and fuel mixture is the Otto engine and has spark ignition.

The Diesel has no throttle it always induces a full charge of air. Fuel is delivered near TDC in a quantity set by the accelerator pedal.

All automotive Diesels I know of are direct injection. Some had a separate ball shaped combustion chamber ported of the head. The injection pump and injectors made Diesels very expensive compared to carburetors fuel system and points ignition of the petrol Otto engine. The mechanical injection pump and injectors have been supplanted in the last 30 years by ECU controlled common rail injection.

Direct injection on petrol of cars is also quite recent. There was a period of about 20 years (1980-2000) where port injection replaced carburetors, injection could be 85-90% of the whole cycle at high load. Direct injection on petrol engines works in 2 modes. One mode it injects like a diesel late in the compression and the fuel self ignites, this is used at low power and moderate cruise. The high load mode injection of fuel will start on induction stroke after the exhaust valve has shut and continue for most of compression when it's ignited by a spark.

patiently explained, well done.

I think all diesel engines of a reasonable size compress air only, and inject fuel either directly into the cylinder, or indirectly into a pre-combustion chamber operating at the same pressure. These are essentially two systems for mixing the fuel and air as it burns.

Ignition timing is controlled by the injection pump. This as well as the more robust construction (necessitated by the higher compression ratio compared with petrol engines) is the primary manufacturing expense.

By comparison, diesel engines for model aircraft are built with only a few cc capacity and rely purely on compression ignition of a fuel-air mixture. They are therefore simper than a comparable petrol engine.

There are "petrol" engines of similar size, usually fuelled with a mixture of methanol and nitromethane, which use a glow plug for ignition. This is pre-heated electrically and is generally contructed using platinum. Ongoing combustion maintains its temperature and the platinum is a catalyst enabling combustion. Timing is controlled by the air/fuel mixture, and the ratio of methanol to nitromethane.

These designs are 2-stroke, so have no camshaft or valves; and the eletrical supply is only required for starting so is not carried on the aircraft or whatever. For capacities above about 30cc it becomes possible to include valvegear and spark ignition so this is typical for chainsaws, lawn mowers, or motorbikes.

Petrol engines can still be injected, either by injection into the inlet manifold or directly into the combustion chamber; but this is to manage proper air/fuel mixing and fuel metering. It is also independent of gravity so ideal for use in aircraft where a float chamber to control fuel flow would give problems, though there were compromise carburettor designs during WW2 used to mitigate the problem.

After removing power to an ECU don't they have to go through a short re-learning routine to match the engine and your driving style? The re-learning is often the first 15 minutes after reconnecting the power and requires the car to be driven rather than just idling.

and a woman designed the workaround

there are a few steps, including coding the injectors. It would be ill advised just to fit one and hope.

That is a little surprising for the time- there wouldn't have been many women engineers. (I'm not suggesting women don't make good engineers - just recognising the way things were. ) Do you know her name please, a useful example to have.

Just in case Mr Cheerful is otherwise engaged I think he may have in mind:

Miss Shilling's Orifice. A restriction in the fuel line that limited fuel flow to max power fuel. 109's had fuel injection and were getting away by diving sharply. The negative G caused the float system in the Merlin's carb to flood the carb. As the sharp dive would be in pursuit it would be at full throttle so max throttle fuel flow was needed and excess fuel from a flooded carb would make the engine splutter and cut out. She also supervised the teams of fitters that went out on squadron to fit the mod.

Before that British fighters had to do a roll into the dive to keep positive G on the float system but that still slowed them up, though not as badly as having the engine cut out. There was scene in "The Battle of Britain" where the the roll into a dive was explained.

Miss "Tilly" Shilling. Holder of a Brooklands Gold Star for lapping Brooklands at over 100 mph. Told her fiance that he had to get one too as she wasn't going to marry anyone that wasn't her equal. Disconcerted friends by having dismembered Norton's in the kitchen.

Thank you.

I'd not heard of her.

A remarkable lady.

She was a remarkable lady. She would have made an excellent dinner guest or after dinner speaker- just think of the stories she could relate!

The "The Tilly orifice"

Mrs Shilling's orifice; well worth reading up about her: