ss2016
Member
This question is just for my education. I am not considering there to be a problem with my engine.
I know quite a bit about carburated aero engines but little about marine turbo diesels.
The two photos below are from April (rpm 2879) and a few days ago (rpm 2875). As you can see all the parameters are very similar except for the boost pressure. 15psi in April and 18psi in September. I am wondering why and how the boost pressure can be higher? In April the bottom would have been clean. Now in September there will of course be some slime on the prop and hull. This though surely is accounted for by a drop in speed through the water. 24Kt > 23Kt
Since the rpm is constant surely the fuel air through the engine is constant. I can see if you put more fuel in you could keep the fuel/air ratio constant if you increased the boost, but since the turbo is free spinning driven by the exhaust why would it increase boost?
I presume the throttle on a diesel is not in fact a throttle but controlling the amount of fuel through the injectors? Does increasing the fuel input increase the power somewhat, but briefly the ratio goes rich, the exhaust volume increase so the turbo works harder so rpm rises bringing the air/fuel ratio back to the ideal? Is this what is happening? Is there any control on the turbo?
I will add the LPH to the display for future reference.
Here we have a constant rpm though, so surely the volume of fuel and air is constant, or has it increased to partly account for the slime as well as the loss of speed?
PS I am not sure it is relevant to the query but the engine in question is a VP D6-400.
PPS I am going to keep a spring/autumn record to look out for changes/problems.
I know quite a bit about carburated aero engines but little about marine turbo diesels.
The two photos below are from April (rpm 2879) and a few days ago (rpm 2875). As you can see all the parameters are very similar except for the boost pressure. 15psi in April and 18psi in September. I am wondering why and how the boost pressure can be higher? In April the bottom would have been clean. Now in September there will of course be some slime on the prop and hull. This though surely is accounted for by a drop in speed through the water. 24Kt > 23Kt
Since the rpm is constant surely the fuel air through the engine is constant. I can see if you put more fuel in you could keep the fuel/air ratio constant if you increased the boost, but since the turbo is free spinning driven by the exhaust why would it increase boost?
I presume the throttle on a diesel is not in fact a throttle but controlling the amount of fuel through the injectors? Does increasing the fuel input increase the power somewhat, but briefly the ratio goes rich, the exhaust volume increase so the turbo works harder so rpm rises bringing the air/fuel ratio back to the ideal? Is this what is happening? Is there any control on the turbo?
I will add the LPH to the display for future reference.
Here we have a constant rpm though, so surely the volume of fuel and air is constant, or has it increased to partly account for the slime as well as the loss of speed?
PS I am not sure it is relevant to the query but the engine in question is a VP D6-400.
PPS I am going to keep a spring/autumn record to look out for changes/problems.
