Originally Posted by AC-AERO
Bill I sent you a reply asking you to clarify your comment about the "poor" frictional issues. I have just come off the dyno with a client and in fact the the FMEP is lower than any engine we have tested to date. Whilst the pumping piston does increase pumping losses and increase friction, this is offset by the fact that these engines do NOT have any valve train rockers or cams to drive.
That is outstanding, Andy, the modern rings must be part of that equation too. I was speaking from a generalization, and that is always dangerous to compare to real life. Yes, the pumping losses are higher, not much available to avoid that, but elimination of a blower for starting to force the beginning of the process is a huge weight saving not to mention friction and pumping losses for some operating conditions. Then there is that thorny heat of compression to deal with . . .
Regarding the expansion ratio, my comment was based on many simulations with piston port valving. (I don't recall the stepped piston design specifically) Where it takes some physical stroke to uncover the port on the expansion stroke. Without 3000 psi PCP capability it is not likely to eat much efficiency, but will definitely have its effect. It might be an advantage for turbocharging, though recapturing the blowdown energy.
Does your stepped design allow tailoring the intake timing to allow a shorter stroke than the exhaust stroke? I am not sure that is even possible as blowdown pressures on 4-strokes can be 50 psi.
All this is moot now with test data coming in. Decades ago I did a tour of Hino, Isuzu Diesel, Toyota, and Mazada, then later worked with Isuzu quite closely. All on diesel designs for low particulate emissions. There are some outstanding diesel engine design engineers close to you!!. The Hino guys were really impressive, as was the designer at Isuzu (Duramax), very free thinkers. All long gone by now, but surely succeeded by people just as capable.
I assume you are using common rail fuel injection? It is the holy grail for multi fuel capability with its ability to rate shape the injection charge and do a pre-injection for control of cylinder pressure rate-of-rise issues.
Best of luck with development, and keep us posted on results. My PM-email works here.