But the bottom line is, avgas is on it's way out. There's no good alternative available yet, and when there is, you can be sure it will be very expensive. Diesel's coming, whether you're a "believer" or not.
Too bad the article doesn't hint at the config, only that it will be easy to use, low priced, low consumption, low weight and (reading between the lines) that it will dispense gumdrops if flying over kindergartens.
Diesel has the inherent advantage of not being reliant on electric spark and having good low rpm torque. Yet factory installations such as Thielert and Diamond's new mill Austro are FADEC, reduction box configs. Forced induction and liquid cooling are complications enough in my opinion, mechanical injection and direct drive should be a given.
I know WAMs are direct drive but apart from the glow plugs I'm not sure they need electrons to inject fuel. Deltahawk certainly doesn't but obviously they need to get flying in a customer installation before the simpler design can be properly marketed to all the diesel thirsty European flying clubs.
Abstract
The paper presents a numerical study aimed at converting a commercial lightweight 2-Stroke Indirect Injection (IDI) Diesel aircraft engine to Direct Injection(DI). First, a CFD-1D model of the IDI engine was built and calibrated against experiments at the dynamometer bench. This model is the baseline for the comparison between the IDI and the DI combustion systems. The DI chamber design was supported by extensive 3D-CFD simulations, using a customized version of the KIVA-3V code. Once a satisfactory combustion system was identified, its heat release and wall transfer patterns were entered in the CFD-1D model, and a comparison between the IDI and the DI engine was performed, considering the same Air-Fuel Ratio limit. It was found that the DI combustion system yields several advantages: better take-off performance (higher power output), lower fuel consumption at cruise conditions, improved altitude performance, reduced cooling requirements. Furthermore, the injection system requirements for DI combustion can be met also by mechanical pump and injectors.
Maybe...maybe not. Even if 100LL is gone in 20 years does not man that diesel is the primary GA fuel. If you do something to force a 100% conversion to diesel/Jet A you kill GA.
There is a reason that auto/truck engines are primarily gasoline in the USA. I don't know the reason but don't expect diesel to become the primary engine in the USA.
Assuming that these folks come up with a product. How long would reasonable people wait until buying one to let initial developmental problems get resolved and reliability established? 10 years, 15? 20?
The only reason diesels have become so popular in Europe is from the massive fuel excise/tax subsidies in mainland Europe. I don't know what it's like now, but historically, diesel has been 50-70% of the price of gasoline in France, Germany, Italy and other places.
If this wasn't the case, Europe would still be as gasoline as the US is and common-rail diesel engine technology would be a passing note in a 1930's technology handbook... (yes really!)
The more I read what's in the science pipeline, the more I become convinced that diesel aircraft engines are simply a niche transitional product. I'm betting that batteries sufficient for cross-country flying will be available within a decade - or less time than I expect my current IO-320 to last.
I would like to see develpment of an aircooled, direct drive, pushrod, flat 4 using mogas, direct injection, and full electronic ignition with the appropriate algorithms built in to automatically lean and richen when necessary. It would be light, cheap, reliable, and efficient.
Tim
I think battery operation is the same as what you say for Diesel, a transitional product. I'm betting that the final thing in the future will be the fuel cell powering the much more efficient electric motor. The nice thing about a fuel cell is that it will be powered with a fuel that can be pumped into the tanks at your airport. Batteries are nice, but not very practical.
The other big win will be that once solar cells break a certain level of efficiency at a certain manufacturing cost, they become cheaper than the cost of simply pumping oil out of the ground. Once that happens, NO ONE will bother with oil - except perhaps as a lubricant.