Expert: Todd Lambert - 5/22/2011

Question
QUESTION: What does nozzle pressure mean? What are the effects of reducing or increasing it on the engine?

ANSWER: Sarthak,

I am unfamiliar with the term "nozzle pressure", but my best guess would be that it has something to do with the pressure at which the injectors inject their fuel into the engine.
What car is this term in relation to? Any more details would be helpful.

-Todd

---------- FOLLOW-UP ----------

QUESTION: Yes, it is the pressure at the injectors. I am asking in general in both, petrol as well as diesel engines.

Answer
On a multi point fuel injection engine the fuel is injected directly into the manifold. The amount of fuel injected is relative to the condition of the engine (the faster the engine is revolving the more fuel is injected). So to reduce the pressure of the fuel injection would be to reduce the amount of fuel being injected, this causing the engine to run poorly. Increasing the pressure would make the fuel mixture too rich and would also cause the engine to run poorly.
I believe that injectors are designed to operate at specific pressures, when the computer alters the amount of fuel entering the engine, it alters the volume of fuel being injected into the engine, not the pressure at which the injector operates.
Diesel injectors operate at a far higher pressure than that of petrol engines because of the far higher rate of compression in the cylinder.

Hopefully this helped.
Let me know if there's anything I can elaborate on further.

-Todd.