Cox (and other model engines) and Diesel

[Johnny L.A.]

I didn't want to hijack the Diesel Engine thread.

As I understand it, a Diesel engine works by compressing a fuel/air mixture until it reaches the point of ignition. I also understand that Diesel engines have "glow plugs".

Model engines such as Cox, O.S., et al use a glow plug to ignite the fuel. (Yes, there are four-stroke model engines and model engines with spark plugs, but most are the glow-plug type.) Once the battery is removed, it seems to me that the heat and compression generated by the engine is what keeps it running.

So. Are model engines really Diesel engines?

[Una Persson]

Well, a good question. People like Heywood define a Diesel engine as being one that burns diesel fuel (duh), uses autoignition after a very short delay at maximum engine compression to ignite the fuel, and of course features a very high compression ratio (12:1 to 24:1). Just by the fact that the model engines in question do not use diesel fuel one could thus easily say that no, they are not diesel engines per se. But otherwise, I see your point. I will look for a more exact definition when I get to my reference books.

[DataMike]

In fact 2-stroke model airplane engines ARE a type of diesel engine, depending on your definition of a diesel engine. ;-)

The way I remember it:

2-stroke model airplane engine: clip battery to glow plug, start engine, remove battery. Engine keeps running due to heat and compression causing glow element (platinum) to glow enough to combust (even when battery is unattached). This is different from a 'true' diesel in that the heat generated by compression is alone enough to cause combustion. True diesel engines (like cars or trucks) use glow plugs only for ease of starting.

BTW, 4-stroke model engines also use glow plugs, they just add a camshaft and valve train.

Hope this helps or at least generates a vociferous refutation.

[GaryM]

[quote]Originally posted by DataMike
In fact 2-stroke model airplane engines ARE a type of diesel engine, depending on your definition of a diesel engine. ;-)

The way I remember it:

2-stroke model airplane engine: clip battery to glow plug, start engine, remove battery. Engine keeps running due to heat and compression causing glow element (platinum) to glow enough to combust (even when battery is unattached). This is different from a 'true' diesel in that the heat generated by compression is alone enough to cause combustion. True diesel engines (like cars or trucks) use glow plugs only for ease of starting.

BTW, 4-stroke model engines also use glow plugs, they just add a camshaft and valve train.

[/QUOTE

DataMike remembers it about the same way I do. I had owned several diesels during my "model airplane years", but never had much sucess geting them to run well.

The heat of combustion in the glow engines keeping the filiment hot is the difference. No hot filiment, no ignition.