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Spark-ignition Distallate Fuel Engine?

Tue Dec 21, 2010 4:56 am

Can someone explain the basic design and workings of a spark-ignition distallate fuel engine? The context where I first encountered the term is the 900hp powerplant of one of the first non-steam powered streamlined passenger train locomotives, the Union Pacific's M-10000 of 1934...and that, in changing from steam-power, the railroad chose to avoid the still unknown (back then) reliability of diesel engine power for locomotives.

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RE: Spark-ignition Distallate Fuel Engine?

Tue Dec 21, 2010 6:42 am

Quoting Tango-Bravo (Thread starter):
Can someone explain the basic design and workings of a spark-ignition distallate fuel engine?

From what I gather, it is just a normal internal combustion engine using a different fuel. Based on the Wikipedia articles it seems that the fuel was not diesel, but rather something similar to the fuel oil used by ships of the era. Of course, this engine obviously used a spark ignition system, rather than the compression system commonly found in diesel engines.

I'm not sure about the unreliability of diesel engines back then. It may have had more to do with diesel's lack of popularity in the US at the time, since it did not become popular here until after WWII. At the time diesel was becoming more and more common in Europe, and Germany in particular powered much of their military equipment with diesel during WWII.
Why do Aerospace Engineering students have to turn things in on time?
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RE: Spark-ignition Distallate Fuel Engine?

Wed Dec 22, 2010 3:20 am

Just a gas engine that was designed to work on kerosene (or gas, until it warmed up)
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RE: Spark-ignition Distallate Fuel Engine?

Wed Dec 22, 2010 3:23 am

We tend to think of the differences between a gasoline (Otto cycle) engine and a Diesel engine as using a different fuel and a different method of ignition -- but there is a deeper difference. In an (idealized) Otto cycle, the addition of heat is under constant volume (the compressed mixture burns mostly near TDC). In an (idealized) Diesel cycle, the heat addition is under constant pressure (the fuel burns during the down-stroke as fuel is injected). The net effect of this difference is that for a given peak pressure, the Diesel cycle can operate at a higher compression ratio, making it more efficient. This means that for a given peak pressure, a Diesel engine could operate at a higher compression ratio than a comparable Otto cycle even without the engine having a stronger construction. Typically though, because there isn't a problem with detonation because of the nature of the fuel and the constant pressure burning, Diesels can even kick it up another notch with even higher compression ratios and peak pressure, though it then requires stronger construction at that point.

Constant-pressure combustion (a la Diesel) requires a high-pressure injection system to overcome compression and combustion pressure -- another main difference with the Otto cycle which mixes fuel with air before compression or combustion.

Also, Diesel engines don't have a throttle, their air flow is fixed (for a given speed) and the power output is regulated by fuel flow only. This eliminates throttling losses which is another advantage of the Diesel.

So, taking an Otto cycle (spark ignition) engine and burning distillate instead of gasoline doesn't really give the engine any of the advantages of the diesel, so I'm not sure why they'd did that -- maybe there's some advantage in terms of fuel handling. Distillate has a higher density than gasoline, so can carry more energy for a given volume of fuel. It's less volatile than gasoline, maybe that's also an advantage in some way.

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