Air pollution in India and also global warming are two major concern in the country. To address this situation, India is moving from BS-IV to BS-VI for on-road applications with 90% reduction in NOx and 50% in PM with limit on particulate number. Also moving to Trem-IV and Trem-V for off-road applications subsequently. It needs higher efficiency after-treatment systems like SCR and DPF to achieve such lower emission levels. Addition of these complex after-treatment system, severely increase the cost of diesel power plant with heavy penalty on fuel economy. Hence, it is challenge to auto industry to reduce the complexity and cost, so that it requires an alternate solution to reduce NOx and PM emissions at source to reduce cost and system complexity. Low Temperature Combustion (LTC) is a potential concept to reduce the NOx and PM emissions simultaneously. LTC concept was experimentally demonstrated on engines of passenger car and light commercial segments, but not much work carried out for heavy duty engines.
The current research work focused on development of LTC concept to reduce both NOx and PM emissions to a required low levels with fuel efficiency improvement so that aftertreatment system cost and complexity will be reduced to a great extent for BS-VI norms. Extensive simulation work carried out in this research for selecting the combustion system including fuel injection system (nozzle configuration, injection pressures and multiple injection), air handling system (air-fuel ratio, EGR%, and swirl) and piston bowl (combustion bowl geometry, compression ratio) suitable to run the engine on both LTC and conventional modes. Engine was built with all modified features and experiments were performed as per BS-VI cycles (WHSC and WHTC).
Experiments carried out over entire engine operating zone with smooth transition between LTC modes in part loads and conventional combustion mode in high load zone. Cycle engine out emissions reduced up to 2.1 g/kWh NOx and ~0.03 g/kWh PM with ~5% overall cycle BSFC improvement in steady state WHSC cycle. Encouraging results have been achieved on transient WHTC cycle also. The lowest BSFC noticed during experiments was close to 191 g/kWh at optimized engine out NOx levels. Utmost important is reduced engine out emissions and improved fuel economy which reduces after-treatment system cost & complexity, operating, maintenance cost and improved field performance with increased regeneration intervals. This result in lower urea and fuel consumption. In summary, LTC is a cost effective solution for BS-VI.
