Yesterday, I had the opportunity to drive a hot-rodded truck. It was a Ford F-350 with the power-stroke 7.3 pushrod turbodiesel.
I noticed the truck had rather quick response time for a turbo, and spine cracking acceleration for a diesel.
Looking under the hood, I found a nitrous oxide solenoid attached to the intake manifold.
WOW.
I know that nitrous adds extra oxygen to the intake charge, which in turn creates more power to the engine.
Nitrous also chills the intake charge of air, making it denser. (N2O comes out of the bottle below freezing.)
However, a diesel operates on compression ignition:
As a gas is compressed, its temerature rises.
At around 15/1 compression ratio, the air in the compressed
cylinder is heated high enough to auto-ignite the injected fuel.
If nitrous Chills the incoming charge of air in a diesel, wouldn’t it lower the compression temp below auto-ignite and stop the engine?
Hopefully Anthracite or one of our other more mechanically experienced dopers will be along in a few here to correct me if I’m wrong, but…
I bet the engine in question has a glow-plug in the cylinder. A glow-plug is like a spark-plug sort of, but instead of sparking, it just stays red-hot all the time by virtue of a steady electrical current running through it. It provides enough heat so that almost no matter what the temperature of the incoming fuel/air mix, there will be an object in the combustion chamber hot enough to ignite the mixture when it gets compressed.
Maybe I’m wrong, I dunno. Maybe the engine control electronics are simply smart enough to notice the temperature of the intake charge dropping and lean the mixture out enough so that the cylinder will still fire anyway. But my bets are on the glow plug…
-Ben
Diesels use propane, not nitrous. Google, “diesel propane shot”, everything on the first page appears to be selling the systems, but there’s a FAQ toward the bottom of this page.
I was under the impression the glow plugs are only used for start-up. Are there some engines which need them constantly on? In the latter case, would this be a factory specification, or the result of customisation aimed at hotting up performance?
Well, there are many things about tuning an engine like that that would be speculation on my part. Yes, some diesels do run with glow plugs on all the time, mainly in high-power applications.
One thing you are missing is the fact that if there is more mass of air in the cylinder (due to increased density), then there is more heat release from the combustion cycle (assuming that more fuel is supplied as well). Overall, one would have to know many things, such as the rate of nitrous (or propane) flow into the engine relative to the rate of air and fuel, ambient temperature, etc. Even gasoline engines sometimes have problems due to the cold air freezing moisture on parts, so it is likely they are not using that much nitrous or propane, or that they just have it very well-tuned.
Auto-ignition ratio is more like 17:1 to 22:1 in practice, not that that changes anything here really…
It may have been a NO control, but I have to wonder at the sensibility of using nitrous oxide and a turbo. I’m not an engineer, but I’d suspect the compression ratios that would result were never anticipated when the engine block was spec’ed (wall thickness, bearings, rods, etc.).
Supercooling and then further compressing intake air (turbo) has to result in forces that would (at a minimum)reduce the life of the block/rings/rods, or worst case blow it all to hell in one blazing fog of cast iron shrapnel.