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Biodiesel is an emerging alternative to fossil diesel for use in compression ignition engines. From environmental standpoint, an increase in nitric oxide (NO) emission from biodiesel fueled engine has been a major concern. Several investigations suggest the role of unsaturated methyl ester as a contributor to biodiesel-NO penalty. The chemical simplicity of biodiesel compared to fossil diesel makes their composition effects amenable to a systematic analysis. In this study, the effects of saturated palm and unsaturated karanja (Pongamia pinnata) biodiesels and their blends (Bio-mix) on compression ignition engine performance, combustion and NO emission are investigated. The combustion and emission characteristics of these fuels are compared with fossil diesel that the neat biodiesel fuels result in improved exhaust emissions except NO with a penalty in fuel economy.

There are several physico-chemical processes which affect diesel combustion. Among them the processes occurring prior to the ignition have significant influence on the combustion and emission characteristics of direct injection diesel engine. The premixed phase combustion appearing between the ignition delay period and the mixing controlled combustion phase has been recognized to be important from emission standpoint. The fuel mass fractions burned in the premixed phase is dependent on the mass preparation rate during the delay period. Based on this consideration, a gas jet multizone phenomenological model has been used for the investigation concerning the premixed combustion phase. The results concerning effect of important engine parameters viz. injection timing, injection pressure and engine speed are discussed in this paper. The effects of these parameters on engine emissions are inferred from the mass fractions burned at the ignition.

Hydrocarbon emissions due to short-circuiting of the fresh charge during scavenging process is a major source of pollution from the two-stroke spark ignition engines. This work presents a prediction scheme for analysis of hydrocarbon emission based on the material balance considerations. A generalized form of globular combustion equation has been used for general applicability of the scheme to any fuel or fuel blends. The influence of mixture quality, scavenging characteristics, residual contents and the delivery ratio are predicted. A good qualitative prediction has been established at all delivery ratios. The predictions are found quantitatively satisfactory in the higher delivery ratio range where the short-circuiting phase of the scavenging process is dominant.

The classical trade-off between NOx and soot emissions from conventional diesel engines has been a limiting factor in meeting ever stringent emission norms. The electronic control of fuel injection in diesel engines emerged as an important strategy for their simultaneous reduction. The high pressure multiple-injection in a common rail direct injection system has been promising in this regard. While, the effects of pilot injection or multiple pulses of CRDI injection schedule on simultaneous reduction of NOx and soot have been widely investigated and reported, the investigations concerning three and more injection pulses have been limited. In this paper, the ability of a predictive model, developed by the authors, in providing optimal multiple-injection schedule is demonstrated through parametric investigations. The effects of pilot and post fuel quantity and dwell between the injection pulses on NOx and soot emissions are discussed.

In this work, a 7.45 cc capacity glow plug based two-stroke engine for mini aircraft applications was evaluated for its performance, emissions and combustion. It uses a fuel containing 65% methanol, 25% castor oil and 10% nitromethane by volume. Since test rigs are not readily available for such small engines, a reaction type test bed with low friction linear and rolling element bearings was developed and used successfully. The propeller of the engine acted as the load and also the flywheel. Pressure time diagrams were recorded using a small piezoelectric pressure transducer. Tests were conducted at two different throttle positions and at various equivalence ratios. The brake thermal efficiency was generally in the range of 4 to 17.5% depending on the equivalence ratio and throttle position. IMEP was between 2 and 4 bar. It was found that only a part of the castor oil that was supplied participated in the combustion process.