Fuel injection time change

[21121956]

Hello everybody:

For stationary medium speed, Miller Cycle engines, burning residual fuel oil Nº 6, in order to improve their performance (mainly with the fuel consumption), some ideas have been proposed.

One of them is to change the fuel injection time. At this moment, the start of injection is at 12º BTDC and, it is proposed to change it to 11º BTDC.

Even when in a general manner I know what happens when the injection time is delayed, I would like to hear your comments in this forum.

Thanks in advance.

 

[Lou Scannon]

I've never heard of a factory engine calibration where timing was advanced of MBT, so what is the rationale for retarding the timing from the factory setting to gain performance/efficiency?

 

[BrianPetersen]

The proposed change is very small, and probably won't have much effect. By the way, MBT = "Minimum advance for Best Torque" which means the least amount of timing advance that still results in maximum torque output, i.e. advancing or retarding from that point results in a loss of torque. Do you know what timing results in maximum torque output for that engine?

 

[Lou Scannon]

I've also seen the interpretation "Maximum Brake Torque", which means about the same thing.

 

[GregLocock]

Ah, and I thought it was Mean Best Torque.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[21121956]

Hello everybody:

Thanks to all for your comments.

BrianPetersen: actually, I do not know what is the timing for the maximum torque output for these engines.

In the beginning of commercial operations that timing was 11,4º BTDC. Almost a couple of years later, the manufacturer recommended to change it to 12º in order to improve the performance.

Nowadays, after a lot of gathered experience (and not a few problems) some people are suggesting to return back to 11º.

 

[Lou Scannon]

Assuming timing is in the MBT region to begin with, retarding a small amount (1°)will tend to reduce most of the stress factors on the engine, with little measurable effect on performance.