How does a diesel engine “know” when to fire?
Since diesel engines have no ignition systems, the fuel is injected into the engine and must ’swirl’ into the highly compressed air at the top of the compression cycle. But how does the ensuing explosion occur at the optimum time?
Diesels dont have spark plugs. The explosion occurs based on compression, which is higest at the top of the compression stroke. Diesel engines use compression ignition where fuel is injected after the air is compressed in the combustion chamber and this causes the fuel to ignite.
Explanation of diesel engines: http://en.wikipedia.org/wiki/Diesel_engine
The fuel is under high pressure depending on which engine you are talking about, On a common rail system it has a rail that is already supply with high pressure then a rocker or a electrical solnoid force a plunger in the injector and the fuel is atomized thru the restriction in the injector tip, diesel fuel is only flammable when it is atomized, the timming works about the same as it would in your car, but instead of the spark plug lighting just before or at top dead center, the injector is typically starting to spray just after the crank is done roatating from the intake stroke, the when the piston is at its peak of stroke the internal combustion reaches extreme temps and causes a internal explsion in the cylnider thus being the power stroke