How Does Engine Power Affect Fuel Mass Flow Rate in Diesel Engines?

AI Thread Summary
Engine power affects fuel mass flow rate in diesel engines, showing a linear relationship up to about 75% load, after which the increase becomes more pronounced. This behavior suggests that higher fuel volumes require longer injection times, leading to inefficiencies. A graph presented indicates that at full load, the fuel mass flow rate deviates from the linear trend, potentially due to increased engine friction. Mechanical losses can be estimated by extrapolating the low power end of the Willans line to zero fuel consumption, revealing friction losses between 2 kW and 4 kW. Understanding these dynamics is crucial for optimizing diesel engine performance.
Alex91
Messages
6
Reaction score
0
Hi

I have been plotting a Willans line, (engine power against fuel mass flow rate) and I noticed that the line is fairly linear up to about 75% and then it starts to increase a bit more dramatically.

  • So I was wondering how does engine power at a fixed RPM effect fuel mass flow rate?
  • Is it directly proportional or is it squared? And how would you prove this?
  • Is there an equation that you can use that shows how the two affect each other?

Any Help is much appreciated.

Cheers

Alex
 
Engineering news on Phys.org
Alex91 said:
… then it starts to increase a bit more dramatically.
Which increases, the power or the fuel flow?
It would help if you could post a copy of the graph with annotations on the scales.

High fuel flow will require a greater time to inject so it will not be as efficient.
 
Hi,

Thanks for the reply.

I have attached a graph of the power against fuel mass flow rate at 1000rpm.

As the engine reaches it's full load, the fuel mass flow rate starts to increase a lot more dramatically. As you can see from the graph, the last four points don't really follow the linear trend of the rest of the graph..

It's almost as if at the very highest loads the engine friction increases a lot more for some reason.

Cheers

Alex
 

Attachments

  • Fuel against power.jpg
    Fuel against power.jpg
    12.3 KB · Views: 636
Your graph shows what looks like a very gentle exponential curve. The curvature is I believe due to the higher fuel volumes requiring a greater period of injection. The line should not be expected to be straight.

Alex91 said:
It's almost as if at the very highest loads the engine friction increases a lot more for some reason.
As the two end points fall below the exponential trend, an opposite conclusion is also possible. I cannot explain those two or three points at the high kW end. It is possible that there could be a significant error in the 14 kW measurement. Whatever the interpretation, it is the wrong end of the graph to yield an estimate of the mechanical losses at the test RPM.

The mechanical losses can be estimated by extrapolating the low power end of the Willans line to zero fuel consumption. The negative x–axis intercept then represents the mechanical power loss. That is the friction of the motor at the test RPM. The extension about the origin is missing from your graph so the extrapolation is not easy. See my attached approximation that shows mechanical losses are somewhere between 2 kW and 4 kW.
 

Attachments

  • extrapolated.jpg
    extrapolated.jpg
    10.9 KB · Views: 672
Here's a video by “driving 4 answers” who seems to me to be well versed on the details of Internal Combustion engines. The video does cover something that's a bit shrouded in 'conspiracy theory', and he touches on that, but of course for phys.org, I'm only interested in the actual science involved. He analyzes the claim of achieving 100 mpg with a 427 cubic inch V8 1970 Ford Galaxy in 1977. Only the fuel supply system was modified. I was surprised that he feels the claim could have been...
TL;DR Summary: Heard in the news about using sonar to locate the sub Hello : After the sinking of the ship near the Greek shores , carrying of alot of people , there was another accident that include 5 tourists and a submarine visiting the titanic , which went missing Some technical notes captured my attention, that there us few sonar devices are hearing sounds repeated every 30 seconds , but they are not able to locate the source Is it possible that the sound waves are reflecting from...
Back
Top