Experimental Study of EGR Mixture Design and its Influence on EGR Distribution Across the Cylinder for NOx – PM Tradeoff

Hardik Lakhlani, Jyotirmoy Barman, Karan Rajput, and Angshuman Goswami
VE Commercial Vehicles Ltd

ABSTRACT

Future emissions regulations like BSIV and above in India, Diesel engine manufacturers are forced to find complex ways to reduce exhaust gas pollutant emissions, in particular NOx and particulate matter (PM). Exhaust gas recirculation (EGR) into the engine intake is an established technology to reduce NOx emissions. The distribution of EGR in each cylinder plays vital role in combustion process and hence it will affect exhaust emissions. The influence of EGR mixture design and its effect on distribution across the cylinder has significant impact on the NOx-PM trade-off which is studied on light duty direct injection diesel engine. A simulation and experimental study of EGR mixer design is conducted to explain this effect and the distribution of EGR across the cylinder at different EGR flow rate. Experiments have been conducted on an engine test bench with and without air-EGR mixer and demonstrated that variations in cylinder-to-cylinder EGR distribution results in a deteriorated NOx-PM trade-off (increased NOx emission level at a given PM emission level, or increased PM emission level at a given NOx emission level) as compared to the well mixed with EGR mixture configuration with equal EGR rate for all the cylinders. The aim of this study is to show that EGR mixture effect & cylinder-to-cylinder variations in EGR can lead to higher NOx and PM emissions as compared to a configuration where the EGR is equally distributed amongst all cylinders. The influence of the NOx-PM trade-off has been experimentally studied in details.

INTRODUCTION

Light-duty trucks play the main role in FMCG logistics and intercity transportation. In India higher subsidy in diesel fuel forced commercial vehicle manufacturers to develop trucks with diesel engines, which are superior for fuel economy and low-end torque due to higher thermal efficiency. Meanwhile, regulations on the harmful diesel exhaust emissions coming out from engines have been increasingly stringent. Meeting BSIV emission norms has become quite complex by introduction of cost effective EGR system in high rating engine. Study of EGR application is very important topic nowadays.

Turbo-charging, high-pressure fuel injection, exhaust gas recirculation (EGR) and exhaust after-treatments have been successfully used in combination to comply with emission legislations of various stages. Among Technical routes to implement emission control, the EGR system is an external device used to control NOx emissions, which has been regarded as an in-engine purification measure for reorganizing the intake and adjusting the in-cylinder combustion process [8, 9].

Engine having EGR emission system where homogeneously exhaust gas mixes with fresh intake charge is very important from the emission & engine fuel consumption point of view. Proper exhaust gas mixing and distribution across cylinder to cylinder will lead to robust engine exhaust gas emission control. The study was conducted on LDT engine's ESC cycle (Figure 15) which had low load, part load & full load with different operating speeds. EGR is one of the most cost effective techniques which are currently available for reducing NOx emissions in internal combustion engines however in the case of diesel engines; they result in worsening of specific fuel consumption and particulate emissions [3, 4, 5].

In particular, EGR aggravates the trade-off between NOx and particulate emissions, especially at high loads. The EGR system reduces NOx emissions by introducing concentration of the exhaust gas into the combustion chamber to increase the heat capacity of mixture hence lower the temperature of burning gases reduce the NOx emission. As EGR would result in the combustion lag and reduced the temperature [10], there is also a possibility that HC, CO, and PM emission would increase. [11].

It is very important in inline multi-cylinder engine that EGR distribution across all cylinders should be uniform. Improper charge (i.e. Fresh air + EGR) distribution leads to uneven charge combustion and unpredictable exhaust emission. Therefore, to achieve the best power performance of engine and the lowest emissions, it is required to figure out a proper EGR rate in each cylinder, by using EGR mixture techniques with EGR system [12].

CONCLUSION

Experiments were carried out to analyze the effect of different multiple injection strategies with EGR system on reduction of emissions, torque and BSFC improvement of 3.7 liters diesel engine. Major findings from this study are summarized as follows:

Related Topics:

EXHAUST GAS RECIRCULATION (EGR)EXHAUST EMISSIONSNITROGEN OXIDESPARTICULATE MATTER (PM)ENVIRONMENTAL REGULATIONS AND STANDARDSDIESEL / COMPRESSION IGNITION ENGINES

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