Investigation on PCCI combustion with cetane improver as secondary fuel for hybrid engine application

• The PCCI combustion helps simultaneous reduction in NOx and smoke, while improving BTE and reducing CO and HC. • Thermal efficiency improved by 4.8 % • Substantial NOx and smoke reduction by 32.2 %, and 32.7 % • The RSM technique is used to predict optimal engine inputs for hybrid engine operation. • Engine inputs of n-heptane energy share and load are established for optimal engine output responses. Premixed charge compression ignition (PCCI) reduces in-cylinder temperatures by transitioning combustion to a more premixed phase. As a consequence, nitrogen oxide (NOx) and smoke emissions reduced. The utilisation of port fuel injected (PFI) n-heptane, a cetane improver as a secondary fuel with direct injected diesel-mahua biodiesel blend improve combustion efficiency and reduce emission. This technique regulate mixture distribution at the compression stroke enabling the charge mixture to auto-ignite, leading to optimal combustion phasing regulating the in-cylinder temperature, peak cylinder pressure (CP), and heat release rate (HRR) across a broad operating range. The heat release process with port premixed n-heptane involved both PCCI and diffusion combustion. The premix ratio significantly influence the combustion and emissions. Though the occurrence of the peak CP and HRR is not affected much, a substantial effect on the values in the diffusion phase is reported. The integration of response surface methodology (RSM) for multi-objective optimization identified engine input parameters for PCCI operation as 28.55 % n-heptane energy share (HES) at 76.13 % load for improved brake thermal efficiency (BTE) by 4.8 %, and decreased hydrocarbon (HC), carbon monoxide (CO), NOx, and smoke by 27.7 %, 36.8 %, 32.2 %, and 32.7 %, respectively over conventional combustion mode. The objective of this study is to determine the strategies for hybrid operation to achieve decarbonisation goals of the automotive industry.