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The matching of fuel injection characteristics with air motion and combustion chamber geometry is now widely modelled for more rigorous investigations of fuel-air, mixing in direct injection (DI) diesel engines to obtain improvements in fuel economy and emission characteristics. A number of studies have contributed in the understanding of fuel spray-air motion interaction in DI diesel engines. The genesis and characterization of swirl motion both during induction and compression is discussed as it influences spray growth, its trajectory and fuel-air mixing. Different aspects of fuel spray structure eg. break-up, drop-size distribution, spray penetration, air entrainment etc. are important. These spray development aspects are also briefly discussed in the paper. Different analytical approaches to model air entrainment in turbulent jet in the engine situation are summarized.

The influence of fuel characteristics on particulate emissions has been widely investigated. In this paper, the effect of different fuel properties on particulate emissions has been reviewed. The effect of fuel sulphur has been reported to have linear-relationship with the sulphate content of particulates. Combustion system, engine loading etc. were found to have weak contribution to the sulphate content variation. The results and analysis of various studies showed that the aromatic content had little influence on particulate emissions particularly in DI engines of modern design. The results from a number of investigations show that the key fuel property influencing particulate matter (PM) is the density.

Two-dimensional Mie and LIEF techniques were applied to investigate the spray formation of a high pressure gasoline swirl injector in a constant volume chamber. The results obtained provide information on the propagation of liquid fuel and fuel vapor for different fuel pressures and ambient conditions. Spray parameters like tip penetration, cone angles and two new defined parameters describing the radial fuel distribution were used to quantify the fuel distributions measured. Simultaneous detection of liquid and vapor fuel was applied to study the influence of ambient temperature, injector temperature and ambient pressure on the evaporating spray.