GOING DEEPER:  IGNITION THEORY

The flame kernel is created when the spark ignites air and fuel in the spark zone.  The remainder of the mixture will be ignited by one of the following conditions:  contact with the flame front; increase in cylinder pressure (which is how a Diesel engine works), or an increase in temperature (which is called pre-ignition if it happens too early).  If the flame kernel is small, the remaining mixture can ignite by itself when the pressure and temperatures rise as a natural response to the existence of the flame kernel.

Perfect combustion would result if all the fuel mixture combusted exactly when the piston held a constant volume in the cylinder.  The Otto-cycle engine operates on this principle.  But in reality, there is a delay between spark breakdown, flame kernel growth, and movement of the flame front across the combustion chamber.  Peak pressure within the combustion chamber should occur when the piston is around 20° after top dead center (ATDC).
Just after the instant of spark breakdown in the combustion chamber, there is a developed flame kernel and the remainder of the unburnt air/fuel mixture.  To ignite the residual air/fuel mixture, the engine system increases the temperature of the remaining gases, raises their pressure, and exposes them to a flame.  A larger flame kernel is exponentially effective because it offeres more mechanisms for heat transfer:  The larger “ball” of the flame kernel has more surface area, so conductive heat transfer is greater.  The larger surface area also imparts a greater radiation heat transfer to the unburnt gases.  Finally, a larger flame kernel that expands at a rapid rate creates much more turbulence, which strongly affects convective heat transfer by tumbling and mixing the remaining air/fuel mixture, exposing more of it to radiative heat transfer.  This means that just a slight increase in flame kernel strength can cause a cascading improvement in the combustion process.  By getting the flame process started earlier, the “mass fraction burned” at any given crank angle position away from TDC is improved. The E3 DiamondFire design burns the air and fuel mixture already in the combustion chamber more completely.  Since the exhaust valve opening occurs at a fixed point in the crank’s position, it is very important to get as much of the fuel burned before it is vented off by the exhaust valve.

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