[LoveLearn]

How vehicle reviewers select vehicle-performance criteria largely determines which configurations they judge to be "best." I keep seeing comments by reviewers who seem almost exclusively driven by MPG considerations which favor configurations which only perform well when judged by that MPG criteria. While that's understandable, I can see merits from developing hybrid systems where the engine's usual operating mode stays close to its lowest Brake Specific Fuel Consumption region, yet retains a robust power reserve available in a higher BSFC region when the driver feels applying more power justifies that higher BSFC cost. Safe passing on 2-lane roads, quicker on-ramp acceleration to more-safely merge with multi-lane traffic and other circumstances argue against entrusting your family's welfare to minimalist engines which, even in an emergency, can develop little more power than is required to sustain steady-state cruising speeds.

Having studied hundreds of BSFC maps, all I've seen generate their lowest (most efficient) values at high throttle settings near their torque peaks. Maximum horsepower in those torque-peak regions where engines develop their best horsepower-hours-per-gallon are greatly reduced compared to their peak horsepower which occurs at higher rpm. I like having a substantial horsepower reserve available even though it requires increasing engine rpm. Through careful planning, we can drive so that's rarely needed. But when (not if) one of those "Oh MY God" moments occurs due to some idiot driver's unexpected behavior, and you need more power right now, I'd be willing to lower my overall fill-up-to-fill-up mpg to keep my family, myself and my property safer. If you have no significant power reserve when you really need it, that long-term maximum mpg at any cost strategy may cost those you love a lot of grief. If you'd have asked me about that 50 years ago, when I had less life experience with idiots on roads, I might also have assigned almost zero value to reserve power for unexpected driving circumstances.

I expect any really well designed diesel-driven electric configuration will be able to reduce engine speed to its least fuel-consumption rpm for the instantly-required throttle-controlled road-horsepower. I expect that diesel will be wonderfully reliable because it will be so ideally loaded, running almost all of the time at low rpms and high throttle settings. Mean time between overhauls for 60-cycle 4-pole direct-drive diesel generator engines which run at 1800 rpm is MUCH longer than mechanical-transmission loaded automotive engines. In Europe, 50-cycle 4-poll direct-drive diesel genset engines run at 1500 rpm also with exceptionally long service lives.

Is sizing a diesel engine so it is most durable "over-sizing?" According to some of this forum's participant's judgment criteria, that would surely be "over-sizing." But that's not my perspective. I like having incredibly durable drive systems with robust reserve power-delivery capacity when I feel it's needed. If that's available with very little extra MPG cost compared to minimalist-sized power systems which can't comfortably cruise coast-to-coast in their torque-peak region, I'd greatly prefer the larger engine pulling the load at lower rpm where it may last 20,000 hours between overhauls.

While I see substantial difficulties in obtaining competitive efficiency from a diesel-electric system, I expect that with equal development effort, it would be more durable than most direct-drive configurations. Diesel-electric rail equipment may not be the most efficient, but it would be hard to fault their durability.

I'm not ready to dismiss diesel-electric configuration cars that don't have a minimalist-sized engines. Without examining any car's on-road BSFC engine loading, I don't see how anyone could intelligently do that.
Just my opinion.
John