Centurion 128-mpg ... and smaller engines
 

128-mpg Diesel-Powered Sports Car

This text rings true to me:
"The technology used to produce Centurion's high fuel economy is very straightforward. An internal combustion engine runs most efficiently when it is operating at 60% to 90% of maximum output. In contrast, when an engine is throttled so it develops only a small portion of its power output capability, fuel economy plummets. Automobiles operate most of the time with the engine throttled to 5% or less of full power, such as when cruising at low speeds in urban traffic. Even on the highway, the average family sedan can cruise at 55 mph on a little as 8 to 10 hp, which is only a fraction of the power capability of the engine. An engine throttled into fractional power regions can use double or triple the fuel per unit of power output. It's as simple as that."

What do you think?

Do you think this had reasonable acceleration? :turtle:

And this text:
"Turbocharging the engine would increase maximum power and performance, and improve fuel economy as well."

I'm thinking turbocharging is key. Could you say turbocharging allows for two powerbands, and two "BSFCs"? How would a gas engine kept in the sweet spot compare to a diesel in efficiency? In other words, what percentage of a diesel's efficiency is due to no throttling?

So, it looks like one needs a non-car/motorcycle engine to achieve 100 mpg with an ICE and no driving tricks.

What might be good sources for used gas and diesel engines of ~20 hp with an appropriate powerband?

Or, if you could get the gear ratios numerically-high enough to have something like a Honda 175 motorcycle engine in its sweet spot (Wiki says "20 bhp @ 10,000 rpm"). That might be more fun- having something that'd rev versus a sewing machine engine.

What do I personally think? Save your $95 and do free research online. That's money that could go toward actually buying yourself a Kubota diesel, a donor car, the tools to do a swap, etc.

As for performance, I can't speak to that. But I would be leery about using a car with a top speed of 65 mph for highway use.

Its pretty significant. Look at a P-V diagram of the Diesel Cycle and the Otto Cycle side by side (especially at part throttle). The lower "loop" of the Otto cycle is pumping losses.

https://wiki.ucl.ac.uk/download/atta...=1240828681000

This is the reason for the Prius using an "Atkinson cycle" engine (not an Atkinson engine). It uses a delayed intake valve closing to allow air to be pushed back out before compression begins. This means it isn't pulling vacuum on the intake side of the engine, increasing efficiency. Toyota also programs the hybrid system to maintain engine load in a sweet spot while charging to maximize efficiency.

This is also the reasoning behind a Hot Air intake (among a few other factors). Hot air is lower in density, which means more is required for a given HP demand. Therefore at a given HP demand, the throttle opening is larger (less pumping loss) than without a hot air intake.

Edit, some more thoughts while I'm still @ lunch...

This is a great argument for a small ICE engine that could operate around 90% power at 80mph - lets say 35hp. Supplement it with a relatively large EV system that can regenbrake and provide acceleration force/hill-climb power and you have a pretty efficient system.

When looking for non-car/motorcycle engines in the small power output range, its common for the BSFC to be pretty crappy by automotive standards (also for them to be dirty). Diesel gensets, lawn equipment, etc. generally use quite low tech carbs and are designed for maximum reliability (neglect), not maximum fuel economy. The also rarely have emissions controls.

Energy density per gallon.

regards Mech

I never considered buying whatever they're selling.

What aboot it?

Pardon my confusion. You quoted and posted a link to a sales pitch, so I assumed you were asking about the product/offering.

how about a modestly powered diesel with propane injection for emergency power needs?

One of the basic reasons why diesels get better mileage. More BTU in the fuel.

You asked.

regards
Mech

1. more BTUs
2. no throttle losses
3. no need to maintain stoichiometry.
4. higher compression ratio

i think that pretty well covers the reasons. there may be more, but, i don't know what they are.