In addition to measuring the amount of fuel and rate of fuel injection, the fuel injection equip-ment must cause these events to occur at the proper time. Correct timing is vital to ensure that complete combustion takes place and that maximum energy is obtained from the fuel. When fuel is injected too early in the cycle, ignition may be delayed because the temperature of the air charge in the cylinder is not high enough. On the other hand, late injection results in rough, noisy operation of the engine. Noisy engine operation occurs when the engine cannot convert as much energy from the fuel into the horsepower required to move the load.
Late injection permits some fuel to be wasted by wetting of the cylinder walls and piston crown.
This condition, of course, results in poor fuel economy, higher than normal exhaust gas temperatures, and smoky exhaust. Atomizing Shortly before the top of the compression stroke, at a point controlled by the mechanical injection timing arrangement, one or more jets of fuel are introduced into the combustion chamber. As explained previously, ignition of fuel does NOT occur immediately on injection. The fuel droplets absorb heat from the compressed air swirling around the combustion chamber. Injection of the remaining volume of fuel for the cylinder continues during this time.