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This study examined a high-speed, high-powered diesel engine featuring a pent-roof combustion chamber and straight ports, with the objective of improving the specific power of the engine while minimizing any increase in the maximum cylinder pressure (Pmax). The market and contemporary society expect improvements in the driving performance of diesel-powered automobiles, and increased specific power so that engine displacement can be reduced, which will lessen CO2 emissions. When specific power is increased through conventional methods accompanied with a considerable increase in Pmax, the engine weight is increased and friction worsens. Therefore, the authors examined new technologies that would allow to minimize any increase in Pmax by raising the rated speed from the 4000 rpm of the baseline engine to 5000 rpm, while maintaining the BMEP of the baseline engine.

Formaldehyde artificially added into hydrocarbon/air mixtures is efficacious as an ignition control medium for the piston engines. The vapor added into the mixtures gives the premixed compression-ignition (HCCI) engine a stable ignition timing. It allows us to get the MBT controllable by the amount of formaldehyde to be added. The added formaldehyde could be a sole controlling factor to the ignition timing. Depending on the temperature to which mixtures are compressed, the effect of formaldehyde adulteration is either suppressing or promoting. The effect of formaldehyde addition is suppressing on the ignition events belonging originally to the cool-flame dominant ignition. In the preflame induction period of cool-flame dominant ignition the added formaldehyde is superfluous to the cool-flame generating processes.