Optimized Combustion, Aftertreatment and Modified Fuel Properties Reduce Fuel Consumption and Emissions: Researchers at the National Institute of Advanced Industrial and Science Technology developed a clean diesel combustion system and identified critical diesel fuel properties to take advantage of the improvements made by both combustion and aftertreatment systems for simultaneous reduction of exhaust emissions and fuel consumption. Combustion control parameters were varied to evaluate their effects on both exhaust emissions and fuel economy in a 9.84-liter, inline six-cylinder, DI diesel engine. The tests were conducted on JIS No. 2 diesel fuel and a modified diesel fuel called CN42. The test parameters were fuel injection timing, fuel injection pressure, and EGR rate. The chapter reports engine control techniques for both JIS No. 2 diesel and the modified fuel and the results of parametric tests conducted under both steady-state and JE05 transient test conditions.