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A phenomenological model for diesel and natural gas dual-fuel combustion for low diesel percentage has been successfully developed. The spray was divided into multiple zones to account for concentration and temperature gradients and stratified entrainment of charge into the spray. Similarly, the premixed “air + NG” burnt gases as combustion progresses were divided into multizones and, hence, could predict the temperature gradients. The combustion model has been validated on available experimental data published in literature. A full-cycle simulation was attempted to evaluate the overall performance of a dual-fuel engine in terms of indicated power at different parametric conditions. The model predictions were compared with experimental pressure time histories and observed to be closely matching.

From the energy security and environment standpoint, the biodiesel fuels derived from vegetable oils or animal fats appear to be promising alternative to fossil diesel. Although the engine experiments prove their viability, the scientific data base for characterizing biodiesel combustion is limited. Detailed studies on the characterization of biodiesel fuels and their effects on fundamental engine processes like droplet evaporation and combustion are essential. The present study evaluates the useful thermo-physical properties and droplet evaporation characteristics of biodiesel fuels. The droplet evaporation measurements are carried out using suspended droplet experiments on five biodiesel fuels of Indian origin viz. jatropha, pongamia (karanja), neem, mahua and palm. The droplet evaporation rates of these fuels are related to properties such as binary diffusivity and molecular weight, which in turn depend on their fatty acid composition.

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.

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.

Fuel-air mixing during the early period has a significant influence on the combustion and emission processes of small diesel engines where combustion duration is short. The mixture heterogeneity during the premixed phase influences the premixed burnt fraction and the peak rate of energy release. The premixed burnt fraction is affected by engine speed, air swirl and fuel injection. In diesel engines, injection parameters, piston configuration and induction swirl interact with each other and have an optimum condition for a better performance. The present paper is an attempt to investigate these effects using an improved existing analytical model. The results concerning the effects of swirl and injection conditions on fuel-air mixing pattern, the premixed mass fraction and the rate of energy release at the instant of ignition, and duration of combustion on engine combustion and emission characteristics are presented.

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.

Based on a multi-zone spray-mixing approach, an air-fuel mixing and combustion model for a Direct Injection Diesel engine is presented. The predictions from the model show very good agreement with the experimental data for various engines under a wide range of operating conditions. Major physical processes are modeled and validated independently. The atomisation process is based on Binary Drop Division concept. Fuel droplets are considered randomly distributed in the spray. A spherico-symmetrical transient drop evaporation model is used for evaporation calculation. A 3-dimensional spray-swirl interaction is modeled on centreline velocity vector/continuum approach. Turbulent mixing is characterised considering all possible available energy sources in DI diesel engines.

A phenomenological model is presented for prediction of the combustion characteristics of a Quiescent Chamber Diesel engine. Predictions with the model have shown acceptable agreement with a range of experimental data. The major physical processes controlling combustion have been characterised, and the dominant role of air entrainment and turbulent mixing confirmed quantitatively.