For the 1990's diesel engines, particulate control has been an important problem.The purpose of this paper is to discuss emission control needs for heavy duty diesel truck engines for the 1990's. This paper will focus on the factors such as fuel injection pressure and fuel properties which most affect particulate emission.The characteristics of diesel spray in the atmosphere and also actual combustion of a turbocharged and charge-cooled H.D. D.I diesel engine were studied as a function of injection pressure ranging from 50 to 150 MPa.Experimental results show that high pressure injection improves the atomization and air entrainment. Though Bosch smoke level, fuel consumption and combustion period decreased with the rise of injection pressure, particulate emission in EPA transient test cycle did not decrease dut to an increase of SOF. With high pressure injection, a reduction of SOF, and consequently, a lowering of particulate emission could be achieved by raising the combustion wall temperature and increasing the compression ratio.Secondarily, the effects of fuel properties, like cetane index, aromatics, sulfur content of fuel and 90% distillation temperature, on particulate and gaseous emission were analyzed. It was found that the reduction of sulfur content, aromatics content, and 90% distillation temperature causes a reduction of particulate emission at EPA transient test cycle.From these results, the reduction of particulate emission can be achieved by not only in-cylinder engine modification but also improvement of fuel properties.