Centurion 128-mpg ... and smaller engines

[drmiller100]

Originally Posted by sgtlethargic

128-mpg Diesel-Powered Sports Car
.

1200 pound car. 20 square feet with decent aero. diesel engine.

I'd bet a hypermiller could get 100mpg, but no way it will get that high in normal driving.

diesels are SURPRISINGLY efficient at lower rates and diesel fuel has quite a bit more energy per gallon then modern gasoline.

Trick is to keep the car light.

And small.

[sgtlethargic]

Is small, light, and aerodynamic gonna do it with a gas engine that's at 20% throttle, even if it's a smaller 4banger?

[drmiller100]

Originally Posted by sgtlethargic

Is small, light, and aerodynamic gonna do it with a gas engine that's at 20% throttle, even if it's a smaller 4banger?

Only one way to find out!!!!!

[Ken Fry]

Originally Posted by sgtlethargic

Is small, light, and aerodynamic gonna do it with a gas engine that's at 20% throttle, even if it's a smaller 4banger?

If by "do it" you mean get 100 mpg, then no, probably not.

Nor will a diesel of enough HP for what most people would consider adequate performance, installed in such a car do it. Jack McCornack is a member here, and has a 32 hp Kubota diesel-powered car of about this size. Prior to going for a better streamlined body, it was getting about 60 MPG at 60 mph. They are now getting almost 80 mpg, apparently, with the better streamlining.

The Riley figures are completely misleading, unless you read the fine print. Nobody else quotes mileage at 35 mph. (The auto manufacturers are not allowed to engage in such shenanigans.) 80 mpg at 60 might be reasonable. 70mpg in a real EPA highway test would be about right. By headlining 128 mpg, they are off to a bad start, so I am skeptical of everything they claim. The streamlining is awful, because the flow will separate as it turns the corner above the back window -- its "all show, no go."

In the VLC from Edison, you can see what is required to get 100mpg in a gasoline-engined car: a very small engine with specialized control to avoid pumping losses, 800 lbs, really excellent aerodynamics, including fully faired-in wheels. I doubt that there is a a diesel engine of around 20 hp that provides the same efficiency as the VLC engine. A 20 HP diesel will weigh twice as much as a 20 hp gas engine, and when new, cost more than twice as much.

Probably the surplus sites, Ebay, and farm equipment junkyards would be good places to look for used (or surplus) 20 hp diesel engines.

[Ragnarok Warrior]

This "Centurion" is from the same company that developed the xr3 XR3 Hybrid Personal Transit Vehicle: A 125 mpg Plug-In Hybrid Three Wheeler You Build From Plans

I would not believe the high mileage on the Centurion because of it's aero. However, given that it is the same company, I believe they use the Kubota D902 engine: 900cc N/A diesel, 25hp @3600rpm (redline), 41 lb-ft of torque @2600rpm (see attached BFSC map.) They attatch this to a VW Type 1 transmission (up to ~'72 beetles/buses.) I believe that would be enough to get a 1000lb car (XR3 without hybrid system) to 125mpg with good aero given proper gearing and driving techniques. I am not so sure that I would believe their BS (nor buy their plans) but the logic is sound, the VW Polo Bluemotion has a curb weight of 2550 lbs and a coeficient of drag of .307 cd and gets around 70mpg with its 1.2?L engine.

The cool thing about using diesel tractor engines is that they are VERY durable/reliable, parts are relatively inexpensive even from the manufacturer due to how common the engines are, and they are very receptive to fuel conversions (veg oil, black diesel, propane, etc.)

As for the turbocharging comment, it is a double edged sword. A turbo will lessen the pumping losses and eliminate throttle plate losses because of boost pressure forcing air into the engine, especially in diesels which run much higher boost pressures than gasoline engines. However, like with anything if you USE the power that it gives, your mileage will suffer because the increase in air will cause in increase in fuel consumption to maintain stoichiometric ratio.

[drmiller100]

diesels don't have throttle plates, nor throttle plate pumping losses.

[pete c]

nor stoichiometry concerns.

i do believe the latest greatest TDs have a throttle plate. Has something to do with emissions. I believe the addition of the throttle plates causes better EGR flow.

i also believe that a properly sized turbo actually increases mileage, assuming of course you have the discipline to not tap into the surplus HP.

[sgtlethargic]

How is the VW 1L prototype getting 170 mpg when 100 mpg seems like a stretch?

[Frank Lee]

Optimization.

[Ragnarok Warrior]

Originally Posted by drmiller100

diesels don't have throttle plates, nor throttle plate pumping losses.

I work at a dealership, although I am not trained as a diesel tech, I do work on the Mercedes OMP 3.0L in the Sprinters and the Cummins engines in Dodge pickups, both of which have throttle plates (electronically controlled, the old 5 cyl inline merc diesel did not.) Also, the lastest VW 16v 2.0 TDI engines have a motorised throttle body and lambda sensors to control egr and air fuel ratio.

Any combustion reaction has a perfect stoichiometric ratio (thermodynamics.) In a diesel there usually is never enough air in the engine to burn all of the fuel that is injected because of design and practical application, however, from my thermodynamics book- diesel will burn in the range of 3:1 all the way to 42:1. This is very different from gasoline which has a perfect ratio of 14.7:1 and will burn from only from about 10:1 to 16:1. The perfect ratio will minimize 5 gas emissions. For example- a gas engine with an afr of 16:1 will produce more NOx gases than one at 14.7:1, an engine with an afr of 10:1 will produce more HC and CO. (see picture) Diesels work the same way, but at different levels/rates but I cannot find a picture.