Hirth 60hp 2-stroke heavy fuel engine with Orbital FlexDI (air-assisted direct injection)

[schmidtproducts]

We can reliably ignite kerosene based fuels such as Jet A, JP5 and JP8. We have done some limited testing on diesel fuel but this has more challenges because it burns dirtier than kerosene fuels.

[amonnaheadbutcha]

what is the maximum viscosity and the maximum density of the fuel that can be burned in this engine?

[schmidtproducts]

The big goal of a "heavy fuel" engine is to support the military's one fuel policy. They would like to eliminate gasoline for logistics and safety reasons. Most Navy ships don't want gasoline on-board because of its volatility. Kerosene based fuels such as Jet A, JP5, JP8 are primarily used in gas turbine or compression ignition engines. Gas turbines are expensive and have high fuel consumption. CI engines are heavy. The DI solution provides a lightweight fuel efficient alternative.

[rustyATV]

Are there performance advantages to running a spark ignition engine on a heavy fuel versus gasoline?

[schlusselmensch]

@rustyATV The main aim is fuel commonality for military use.

[rustyATV]

@schlusselmensch I'm aware of that. But it's also a fact that heavy fuels (diesel, Jet A, JP4, etc) have a greater energy density and gasoline, so it would be interesting to see if there were any difference in power output. I'm actually interested because I have a pipe dream of a heavy fuel two stroke dirt bike motor, if there are gains to be had.

[schlusselmensch]

@rustyATV Heavy fuels have greater energy density but that just means you need a smaller gas tank to go the same distance as something that runs on, say, methanol. It's neither here nor there as far as power output goes.

As far as gains to be had, engineering compromises make that a hard question to answer. There already is a four stroke diesel military motorcycle if you are interested in such things. Unsurprisingly it is somewhat heavier and slower than an equivalent gas engined bike.

[rustyATV]

@schlusselmensch Sure, heavy fuel in a heavy, high compression diesel goes farther than methanol in a light spark ignition engine, but can you be certain the same would apply for heavy fuel in a spark ignition engine? I'd prefer a dyno chart over a speculation

A friend had shown me that bike; based on a Kawasaki KLR650 if I recall. Im more interested in a two stroke diesel, not of the old tractor-trailer or locomotive type, but a reed valve motor like what Yamaha was researching in the late 90s

[schlusselmensch]

@rustyATV Typically, reed valve 2 stroke configuration doesn't have the scavenging capability to really promote efficient combustion. You need to resort to something like the Wulf 2 stroke sytem or you need forced aspiration. It's all been tried by the way, you just have to get into old engine literature. Would the same apply? Certainly; you're consuming hydrocarbon fuel, its energy density is pretty unimportant. So the question is what kind of thermal efficiency can you achieve?

[schlusselmensch]

@schlusselmensch You have to consider that you would not even approach the efficiency of huge 2 stroke marine prime movers (around 50%) would all the effort be worth it? If you think so, get to it Jethro!