Internal combustion engines may run on similar principles, but they don’t all feature the same operating cycles. While many engines feature a four-stroke cycle, comprising intake, compression, expansion-power and exhaust, the Miller Cycle
, originally patented by the American Ralph Miller in 1957 and still used today, differs by having a longer expansion stroke than the compression stroke, which is synonym of better thermodynamic efficiency. This is generally done by closing the intake valves earlier than on a normal engine.
Used alongside a turbocharger or supercharger, the part of the forced induction (cooled compression) into the global compression is larger, leading lower maximal cycle temperatures and better [NOx
emissions and efficiency] trade-off, while improving combustion stability and keeping away the knocking in the case of spark-ignited engines.
Miller Cycle engines can be more efficient as a result.