Diesel Injection Timing

Hey all,

I understand that most modern diesel engines at light load and low rpm will begin injection just after TDC in most applications I've seen. Reasons being, NVH and for emissions.

I noticed in the course, Nick wanted to try make the target power with extra fuel rather than advance SOI.

As a newer diesel tuner, why is this?

Moving SOI around is usually worth very little in the way of additional power unless the engine is under heavy load and is way out of time. A diesel engine is throttle by, and therefore manages its torque output via fuel mass (mg/stroke). Basically when you push the accelerator pedal the engine (instead of adding air via a throttle blade like a gasoline engine) just adds fuel to what is already a very lean combustion situation. So long as the engine is running lean of 1.15-1.2 lambda you can simply add fuel to add power.

Does this help clear things up a bit?

Nick

Thanks Nick,

Yeah that makes sense, I understand all that, I haven't had much of a play with SOI given there's usually so many maps for modes/elevations etc, much the same as injection quantity. One set of multiple tables is enough to modify especially when using HP tuners that doesn't have a "make same changes to similar tables" function.

Heard that, brother. There's a few buttons HPT could stand to add. :)