> Diesel Nitrous: Understanding the difference between Diesel and Petrol Nitrous Oxide Injection (NOS)

Diesel Engines and Nitrous

Diesels can use Nitrous Oxide to supplement their power too. But there are some important differences in the application.

To begin with you cannot inject diesel fuel and Nitrous Oxide into the intake system or ports as you would inject both fuel and Nitrous in a petrol engine.  The reason is simple, the fuel ignites under the compression stroke and does so far too early in the cycle -- way before it should!  This means your engine will either stop dead in its tracks or more likely break something expensive!  Either way you really wouldn't want to try it!

The fuel and nitrous ignites due to the heat of compression rather than at the correct point when the diesel injector fires. Normally there is just air in the cylinder, and the ignition only commences at the correct time as the diesel pump injects the fuel via an injector straight into the cylinder. The Diesel pump effectively controls the timing in the same way as the spark does for a petrol engine.

Adding Diesel fuel the the intake tract is a sure way to drive over your crankshaft.  Adding just Nitrous without extra fuel just wastes the nitrous since there isn't any extra fuel available for it to Oxidize / burn.  So it just gets thrown out of the exhaust.  Doing this in a petrol engine would cause a weak mixture. Doing this in a diesel engine does not.

Diesels ALWAYS run "weak" so to speak since they always induct a full cylinder full of air as there's no throttle plate!  Even at idle. Speed is controlled purely by the amount of fuel injected. They don't actually "run" weak as such, since the fuel enters via the injector at a single point and it always rich at the point of injection since its not evenly spread around the combustion chamber.

So at idle, and at less than full throttle operation much of the air travels through the engine unused. and unburned. At full power all the oxygen and all the fuel is consumed if the diesel pump is set up correctly.  So if the diesel is set up any richer on purpose it just smokes. Because now all the air is used up, so the extra fuel goes out of the exhaust unburned.  Now what happens if we add more oxygen (or rather Nitrous Oxide) while it runs rich and sooty?  That's right, clean exhaust again and more power.

So to add extra enrichment fuel to a diesel you need to do one of several things:

a) You add a fuel to the air intake that does not ignite under the heat of compression alone. This can be done with the normal solenoids and nozzle arrangement as you would do in a petrol engine. The difference is that you would use Propane gas instead of Diesel. Now the propane is high octane and has a high self ignition temperature. It will not ignite early, it will only be ignited by the burning diesel fuel as it is injected at the correct timing point.

b) You do as above with Methanol. Theoretically. Not tried by me so far!  I suspect that it will need to be injected very well atomised by the Nitrous fogger as close to the cylinder head as possible to prevent it condensating or "dropping out" of the airflow.

c) You fool or trick your vehicles existing diesel injection pump into delivering the extra fuel. There are a multitude of ways to do this as there are so many different diesel injection systems around. So that part will be up to you! Only do it when you activate the system.

Don't forget that if you add a lot of nitrous you still need to retard the timing as you do with a petrol engine via the injection pump timing.

Mixture...

Unlike a petrol engine running "weak" does not bother a diesel engine. So adding masses of nitrous with no extra fuel wont do damage. All that happens is that the diesel injected burns away and leaves the rest of the oxygen wasted and dumped through the exhaust.

And running rich with far too much fuel being added either with nitrous or without results in lots of black exhaust smoke as this diesel cannot be burned (soot!) as there was insufficient oxygen available.

So set it up to show traces of black smoke so that you know you are burning as much of the expensive nitrous as possible!