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Engine components are exposed to various lubrication regimes such as hydrodynamic, elasto-hydrodynamic, boundary and mixed lubrication during engine operation. In each of these regimes, the factors which influence engine friction are different. Hydrodynamic friction is influenced by lubricant rheology, film thickness and sliding speed of interacting surfaces, whereas boundary and elasto-hydrodynamic friction is a function of surface properties like roughness and hardness and the type of friction modifier used in engine lubricant. So the principal factors which influence engine friction power are speed, load, surface topography of engine components, oil viscosity, oil temperature and type of friction modifiers used. Experimental studies on an off-highway diesel engine were conducted to investigate the effect of engine oil viscosity and engine operating conditions on engine friction power.

In India, continuous efforts are being made to upgrade fuel quality and vehicle technology for meeting European emission norms. However, these efforts make a very little impact in improving the air quality due to exponential increase in the vehicle population and the poor quality of the Indian roads. The long-term strategy for meeting the requirement of huge road infrastructure and traffic management systems needs immediate attention. Studies have been conducted worldwide to study the effect of fuel quality and vehicle technology on fuel economy and emissions. However, the contribution of road quality, traffic management and driver training on reduction of vehicular emissions and improvement of fuel economy under Indian road conditions is still not established.

Gasoline vapour losses from marketing operations are a major source of Volatile Organic Compounds (VOC) emission and a significant economic loss. Exposure to VOC can cause adverse health effects. VOC also lead to the formation of harmful ground level ozone. Gasoline vapour losses from retail outlets occur in two stages viz., vapour losses from the underground storage tank termed as Stage I and vapour losses during dispensing of fuel to the vehicles termed as Stage II. In India, there are currently only few Stage II vapour recovery systems in selected marketing outlets and no Stage I vapour recovery systems in place. Quantifying the extent of the gasoline losses would help in implementation of the vapour recovery systems.

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.

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.