R35S chamber is a high squish combustion chamber that can reduce smoke and particulate emissions without deterioration of NOx emission compared with standard toroidal shape combustion chamber (STD). STD chamber can emit higher soot emission due to large amount of injected fuel escape from piston bowl to the top clearance from early combustion stage and increase possibility of those fuel to be quenched. R35S chamber can keep the injected fuel remains under the squish lip for long time and restrain more fuel to be quenched at the top clearance. Benefit of using R35S is also extended for utilization of Biofuel. Waste Cooking Oil (WCO) with high density and kinematic viscosity have been tested. High turbulence combustion is effective to reduce SOF and THC emissions of neat WCO fuel at lower load as well as SOLID emission at high load. This is because high turbulence promotes spray droplets evaporation. Moreover, complex air motion reduces spray impingement on the wall, and most fuel burns completely by rapid combustion.