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Variable valve timing allows the effective compression (in cylinder actual) to be controlled with valve duration of both intake and exhaust separately. Variable lift would also allow for the same lower compression.
Direct injection also cools the piston head and cylinder head temperatures.
Higher rates of EGR are another way to control peak combustion temperature.
Fuel injected at TDC and even after TDC in multiple stages are another way to eliminate preignition, since preignition requires the air and fuel to be ignited before the piston reaches TDC. The peak combustion pressure can even be delayed past TDC when a combination of these strategies are employed.
regards
Mech
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