Motor Road Transport For Commercial Purposes
(Liquid Fuel, Steam, Electricity)

40 MOTOR ROAD TRANSPORT retard it for that which. is rich in proportion of fuel to air. Another consideration is that as compression varies in relation to throttle opening so will the rate of combustion. For example, as the throttle is closed, the volume of the intake will be decreased, and, i ft s o facto, the subsequent compression. In this case, unless the firing can be advanced, the combustion will not have been completed before the exhaust valve is opened. Flame Propagation. The difficulty of obtaining purity of exhaust is already great, and because of this a considerable proportion of air in excess of that required tlieoretically for complete combustion must be admitted in order to secure good results. To employ fixed-point ignition is, therefore, to complicate a problem, the solution of which. is already sufficiently difficult. The range within which petrol and air mixtures are explosive as opposed to quiet burning is comparatively small, and the need for ignition at the most favourable moment for rapid spread of the flame will thus be recognized without difficulty. The slower the propagation the gréater the dissipation of heat, since energy is required to raise the temperature of the remaining gases or excess air, while owing to incomplete combustion a smaller quantity of heat is generated than would be the case with a correctly proportioned mixture. At low and high piston speeds the increase of power from an engine fitted with variable ignition over a similar one provided with the fixed type is very marked, and represents a considerable percentage of the total output. How Expert Drivers Reduce Gosts. How does all this affect the van owner ? A driver who Controls the spark and throttle with intelligence