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Hi, Some of the dates and ratings are incorrect. This is probably due to poor data. Unfortunately, that can give very misleading information. As for speculating wildly about this, I don't feel that that is any problem for many people. As always, the devil is in the detail. Eng
Some of the dates are extremely arbitrary.
The other numbers should be good for at least some versions of the engines. Some of these engines were produced in many, many versions.
Not really.BMEP gives you a good idea of what is happening inside the engine cylinder.
Maybe in combination with a crystal ball.BMEP should give you a good idea of what octane fuel they were using, plus the presence of water and/or methanol injection.
IMEP is fairly real if you have a pressure gauge attached to your engine. BMEP is significantly lower than IMEP for reasons that should be obvious.Not really.
IMEP might give some idea.
BMEP and IMEP are ficticious pressures that can only be calculated, not measured.
For a piston engine alone, one can calculate an IMEP.
For the total combination of piston engine plus supercharger, oil pump, magnetos, and friction losses, one can calculate a BMEP
Maybe in combination with a crystal ball.
BMEP also depends on whether a supercharger or a turbocharger is used, whether an intercooler (aka aftercooler) is used.
Moreover engine power depends on altitude.
Note also that British HP is not the same as German HP (PS).
The engine BHP per pound (or kW/kg) is in practice more important than BMEP, but for watercooled engines you should then include the weight of the cooling fluid, piping, radiators, intercooler (if present), et cetera, when comparing with aircooled engines.
If a turbocharger is included that weight plus ducting plus intercooler should also be included for aircooled as well as watercooled engines (P-47 is aircooled with turbocharger, P-38 is watercooled with turbocharger).
If a system for injection of methanol/water or N2O is included that also adds to the weight.
If you like you can make a lot of different comparisons, including this, or excluding that, but be careful not to drive yourself crazy.
The extra fuel acts as a coolant, both for the mixture before ignition and for the cylinder (and parts) in general after ignition. The unburned fuel carries heat out the exhaust valve and out of the engine.Once there is enough fuel to burn all the oxygen in your fuel air mixture, there is no point in adding any more.
BMEP it quite dependent on supercharging.Actually, BMEP is independent of supercharging.
I think we are arguing about what compression really is.Higher compressions, resulting in higher BMEP, are made possible by high octane fuels, which allow more compression, by intercoolers and water methanol injection, which cool the air and allow more compression,
It is pretty straight forward compared to propeller design, it is a dark nether world of satanic magic.
You can't measure IMEP with a pressure gauge.IMEP is fairly real if you have a pressure gauge attached to your engine.
You can't measure IMEP with a pressure gauge.
IMEP is calculated from IHP (indicated horsepower) in the same way as BMEP is calculated from BHP (brake horsepower), and therefor just as fictitious as BMEP. Only of interest to academics.
Difference between IHP and BHP (and consequently between IMEP and BMEP) is the power that is consumed by supercharger, oil pump, magnetos and friction losses, which reduce the available power from IHP down to BHP.
I think the point being made was that you cannot DIRECTLY measure BMEP / IMEP from a gauge.View attachment 723622
Pressure gauge on an engine. This one is 250 cubit inch GM six cylinder running at 2000rpm. The work done per stroke is the area of the big curve minus the area of the small curve. This was all done in college about forty years ago. I understand they still have the engine. This is a polaroid of an oscilloscope output. We saw all sorts of weird and wonderful curves on the oscilloscope. We judged this one to be typical. Don't think you are seeing any sort of precision here.
For the record, IHP, calculated from the pressure gauge output was 115psi. IHP was 72.6. BHP was 52, and BMEP, calculated from rpms, displacement and BHP was 82psi. I have no idea of what condition the engine was in. Given it was in the basement of what was then a polytechnical college, the exhaust system may have been very interesting.,
That is the simple stuff to draw the foolhardy and unwary into their trap. No one has mentioned flame front velocities, rates of expansion of the chamber and the burning fuel or even energy losses. Unplug your computer, immerse it in bleach and walk away, then you will have been saved.It is this kind of explanation why I could never be an engineer. It makes my brain hurt.
Radials often used a BMEP gauge for setting power and for adjusting mixture settings, used on the R-1820 in the S-2 Tracker and R-2800, R-3350, R-4360 installations.I think the point being made was that you cannot DIRECTLY measure BMEP / IMEP from a gauge
Weighing a cut out piece of paper would be more accurate than selecting the most typical polaroid photo of the batch.I think the point being made was that you cannot DIRECTLY measure BMEP / IMEP from a gauge.
You have a lot of work to do here to translate that PV diagram into IMEP (sorry for pun).
You`ll need to integrate the area of the curve then decide if you`ll subract the suction area or not (which
contributes if its forced induction or subtracts if its naturally aspirated)>
It says they used to do this by cutting out the shape on the indicator card then weighing it !
Which if you`ve got some precision card and you remembered to weigh the sheet before you cut it up, is as good a way as any I suppose !