Shamit Bakshi

Common rail direct injection (CRDI) system is a modern variant of direct injection diesel engine featuring higher fuel injection pressure and flexible injection scheduling which involves two or more pulses. Unlike a conventional diesel engine, the CRDI engine provides simultaneous reduction of oxides of nitrogen and smoke with an injection schedule that has optimized start of injection, fuel quantity in each injection pulse, and dwell periods between them. In this paper, the development of a multizone phenomenological model used for predicting combustion and emission characteristics of multiple injection in CRDI diesel engine is presented. The multizone spray configuration with their temperature and composition histories predicted on phenomenological spray growth and mixing considerations helps accurate prediction of engine combustion and emission (nitric oxide and soot) characteristics. The model predictions of combustion and emissions for multiple injection are validated with measured values over a wide range of speed and load conditions. The multizone and the two-zone model are compared and the reasons for better comparisons for the multizone model with experimental data are also explored.

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. The emission predictions from the model are corroborated with available measured data. The comparisons between predicted and available measured data show that while an optimum quantity of pilot fuel reduces NOx emission, the post injection fuel quantity and its dwell from main injection pulse lowers soot emission. © Copyright 2011 Society of Automotive Engineers of Japan, Inc. and SAE International.

The possibility of multiple-injection in Common Rail Direct Injection (CRDI) engine allows achieving improved combination of oxides of nitrogen (NOx) and smoke emissions. In CRDI engines, the turbulent kinetic energy due to high pressure fuel injection is primarily responsible for fuel air mixing and hence the in-cylinder mixture formation. The air fuel mixing characteristics in the case of multiple-injection are quite different from that of single injection schedule. In this work a zero-dimensional model is proposed for mixing rate calculations with multiple-injection scheduling. The model considers generation and dissipation of in-cylinder turbulence through processes namely fuel injection, air swirl and combustion. The model constants are fine tuned with respect to the data available in existing literature. The model predictions are validated with the available data for the cylinder pressure and heat release rate histories on known single and multiple-injection schedules. These comparisons show good agreement to establish the role of mixing rate variations with multiple-injection. A single set of constants were found to match the cylinder pressure and heat release rate histories for single and multiple-injection from different sources in the literature. Further, the mixing rate and peak temperature predictions of the model are found to relate with the possible effect of specific injection scheduling on emission reductions reported in CRDI engine investigations. Copyright © 2009 by ASME.

It is becoming evident that the fuel-air mixing process in high pressure multiple-injection CRDI engines is different from the conventional single injection such that a simultaneous reduction between NOx and soot particulate emissions is realizable. As a novelty, this paper explores the physics behind the mixing processes in multiple-injection technique using a comprehensive phenomenological model developed and validated by the authors for predicting combustion and emissions characteristics of multiple-injection CRDI engines. Towards this objective, the paper predicts and relates the variations in mixing rates for double and triple injection schedules with their observed combustion and emission characteristics. These quantitative predictions of mixing rates in multiple-injection substantiate the cause of soot reduction during later part of CRDI combustion. The predictions of fuel evaporation, fuel air mixing and emission characteristics of high pressure multiple-injection CRDI engines obtained from the model are found to reveal features useful in understanding CRDI engine performance. The trends and relationship of injection and its related processes observed in this study conform to the experimental observations of several multiple-injection CRDI engine studies. The predictions from the model suggest that there must be an optimal injection schedule in order to achieve the simultaneous reduction of nitric oxide and soot particulate emissions with the minimum sacrifice on fuel economy. Copyright © 2012 by the Japan Society of Mechanical Engineers.

The high-pressure multiple injections in common rail direct injection diesel engines offer a possibility of simultaneous reduction of exhaust smoke and oxides of nitrogen. The purpose of the present work is to develop a phenomenological model to enable parametric understanding of the combustion and emission characteristics of multiple-injection common rail direct injection engines. The model is based on a two-zone formulation comprising of fuel-air spray and the surrounding air. The model predictions for combustion and emissions are validated with measured results of different multiple-injection schedules available in the published literature. The effect of parametric variations of multiple-injection scheduling on emission characteristics are predicted using the proposed model. It is observed that the simultaneous reduction of oxides of nitrogen and smoke is possible with an optimized pilot fuel quantity and dwell between the injection pulses. © IMechE 2011.