Quote:
Originally Posted by RustyLugNut
. . . will look at the BMEP equation and realize that any modifications that maximize BMEP will yield more power at the given rpm. The straightforward solutions of more air, more fuel and optimized ignition timing lead to supercharging, higher flow fuel systems and advanced ignition systems with knock sensor feedback. These and other performance modifications certainly result in increased effective cylinder pressure, but which ones are relevant to the goal of the Ecomodder? We do not want to drive around at nearly full throttle all the time, but as many of us know, this is the throttle setting for a spark ignited gasoline engine that results in the best power output for the lowest fuel input or the lowest BSFC ( Brake-specific-fuel-consumption ).
Since we cannot drive around at heavy load, we pulse and glide to get an "average fuel use" that is considerably less than a partially throttled engine driving the same distance. Engine designers have used cylinder de-activation to achieve the same goal but with varying degrees of success.
|
. . . was one that defined the efforts of the three aforementioned Xprize teams. Each of them responded with different solutions.
The Edison team designed a custom engine that could produce power with a wide valley of low BSFC and also leveraged the generous Xprize rules for specific energy content for fuel volume. Building around the high octane inherent in the E85 fuel, their engine propelled their sleek and light weight car to the class win.
Jack McCornack looked at the requirements for hitting 100 MPGe (MPGe was the Xprize way of equalizing all the fuels and their differing make ups ) and decided on the expedient solution of using a current engine that already had low BSFC over a wide range because of no throttling losses - he chose a turbo diesel engine to power his entry car, "Max". Even with the higher diesel energy factor requiring 114 MPGe, his "napkin calculations", coupled with a sleeker fiberglass body and idealized gearing would have allowed Jack to be competitive if he had not been forced to withdraw due to "production" rule changes.
Aptera's offices and labs were only about half an hours drive from my home in San Diego. I considered them one of the front runners in the 2 seater class before technical difficulties not directly due to their brilliant design left them out of contention. They took the simple expedience of not dealing with engine design or selection and simply went with the most efficient drive train available to them - they used an electric/battery drive.
The disappointing part of the Xprize and the after results is the lack of immediate technology transfer to the everyday world. I had hoped an ICE evolution that would carry forward the momentum of engine tech such as the stratified charge engines from Mitsubishi in the 70s, the lean burn engines of the 80s, and the effective Honda Lean Burn VX engines that came after would make an appearance in the competition. Engine technology would transfer the most readily because consumer acceptance of what is under the hood is very broad - if it works, most people really don't care what powers their car. Unfortunately, engine and drive train development is difficult in comparison to light weight and aerodynamic body design and construction. The backyard tinkerer or the small development group would be hard pressed to compete with the large corporations in the time frame provided. And, no large corporate groups committed to compete.
So where does that leave the average Ecomodder and his equation for BMEP?