%X Hydrogenâ��s high flammability, low ignition energy, clean burning, and high flame speed are attractive advantages of using internal combustion engines to attain high performance and efficiency as well as achieving â��realâ�� clean emission with only water and carbon dioxide as exhaust. To overcome volumetric efficiency loss, high NOx emissions and abnormal combustion, the influence of airâ��fuel ratio is studied. Optimization of the airâ��fuel ratio effect and understanding of the combustion processes are actively being studied in the automotive industry and research institutions. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2019. %O cited By 1 %L scholars12273 %K Automotive industry; Carbon dioxide; Ignition; Internal combustion engines, Abnormal combustion; Clean burning; Combustion pro-cess; Direct injection engines; Ignition energies; NOx emissions; Research institutions; Volumetric efficiency, Direct injection %D 2019 %A A.R. Abdul Aziz %A M. Adlan Abdullah %A Firmansyah %A E.Z.Z. Abidin %P 21-36 %I Springer Verlag %R 10.1007/978-981-13-2968-5₂ %T Performance of hydrogen direct injection engine %J SpringerBriefs in Applied Sciences and Technology