FGD135, to take up some points, whether a diesel engine uses diesel or jet fuel (kerosene) is immaterial. The original diesel engine was in fact to use the oil coming straight out of the oil well. Ship diesels use bunker oil which has to be heated in order to get the viscosity low enough in order to pump the stuff. You can not compare aircraft piston engines to motor vehicles. Aircraft engines are big bore and one of the reasons for dual plugs is so that the charge in the cylinder all gets burnt. This is because of the slow speed of the flame front. With only one plug not all the charge would be burnt. The DB engine as fitted to the Me 109, although it had dual plugs, both were installed on the same side of the head, rather than on opposite sides, and the engine suffered some thing like a 10% loss of power as a result. The RPM of an aero engine is limited by the prop aerodynamics (Mach number of the tip), extra horse power can be extracted by increasing RPM, but that then necessitates a gear box to reduce the prop RPM. Added complexity. The Bear bomber has turbo props putting out some 15,000 horse power each with a prop RPM of only 750 and is capable of near jet speeds. Peak pressure does not occur at 90° crank on any internal combustion engine.