Combustion Basics. Main factors influencing the combustion process. Organised combustion. Diesel combustion. Spark ignited combustion. Turbulence. Lean-burn and stratified charge. Swirl stratification. Pre-chamber stratification - Honda CVCC

The Spark Plug. Firing voltage and current. Phases of the spark. Power required for ignition. The spark gap. The spark process. Spark duration. Spark energy. Effect of mixture strength. Spark energy and gap erosion. Vee groove. Platinum electrode. Iridium/platinum. Importance of platinum/iridium electrodes in WW2 aircraft.

Events after the Spark. Pressure curve and burn rate. Ignition lag defined. Effect of turbulence. Alleged limitation of r.p.m. Very high speed miniature engines. Motorcycle engines lead the way to high r.p.m. F1 engines leap ahead. Combustion in a 20,000 r.p.m. F1 engine.

Flame Propagation. Effective burn time. Cylinder pressure. Connecting rod leverage. Angle of maximum effort at crankshaft. Spark timing. Burn rate increase with engine speed. Ideal advance curve. Typical advance at maximum torque. Multiple spark plugs.

Energy Losses. Heat balance diagram. Potential for improvement. Losses to coolant. Effect of charge temperature. Diesel advantage at part load. Rising specific heat of combustion products. Coolant losses vs exhaust losses. Ceramic coatings. Compression and expansion ratio. Higher compression for economy. Final thoughts about timing.