Diesel engines do not have preignition problems because fuel is injected at the end of the compression stroke, therefore higher compression is used.
22.
Furthermore, fuel is injected during the intake stroke and not at the end of the compression stroke as in a Diesel's compression ignition engine.
23.
Knocking is more or less unavoidable in diesel engines, where fuel is injected into highly compressed air towards the end of the compression stroke.
24.
If during the compression stroke the air-fuel mix reaches a temperature greater than the auto-ignition temperature of the fuel, the fuel self or auto-ignites.
25.
When starting from cold, the engine's combustion efficiency is reduced because the cold engine block draws heat out of the cylinder in the compression stroke.
26.
As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled back out through the still-open intake valve.
27.
So in the Miller cycle engine, the piston actually compresses the fuel-air mixture only during the latter 70 % to 80 % of the compression stroke.
28.
During the initial part of the compression stroke, the piston pushes part of the fuel-air mixture through the still-open intake valve, and back into the intake manifold.
29.
Thus, in each revolution, one piston provided a compression stroke and a power stroke, and then the other piston provided an exhaust stroke and a charging stroke.
30.
The temperature at the top of the compression stroke depends on many factors, particularly the compression ratio of the cylinder and the starting temperature of the inducted air.
