Off-road BS III CEV (US-TIER III equivalent) emission regulations for diesel engines (i.e. Construction Equipment Vehicles) in India demands a technology upgrade to achieve a large reduction in NOx (>50%) and Particulate Matter (>50%) compared to BS II CEV emission levels. EGR is a widely accepted technology for NOx reduction in off-road engines due to lower initial and operating costs. But EGR has its own inherent deficiency of poor thermal efficiency due to lack of oxygen and further increase in soot adding complexity of meeting PM Emissions. Hence an engine meeting BS III CEV norms without EGR/SCR technologies with low initial investment is most desired solution for Indian off-road segment.
This work deals with the development of an off-road diesel engine rating from 56 to 74 kW, focused mainly on in-cylinder optimization with the aid of optimum injection and charging strategies. A comprehensive 1D thermodynamic simulation had been carried out to study the effect of engine parameters i.e. injection pressure, no of nozzle holes and hole dimensions, start of injection and boost pressure ratio on performance and emissions. Based on analysis the most suitable DoE (Design of Experiments) factors and levels were selected to minimize the experimental effort.
A full factorial DoE plan has been formulated from the selected factors and levels. Experimental set up capable of performance, emission and combustion measurements was created. Experiments were conducted with performance and emission measurements and optimum parameters were identified. A modified re-entrant bowl with a compression ratio of 17.5:1 was found best suitable with a nozzle having 25% lower hydraulic through flow. The spray plane was found to be optimum with 2.8mm nozzle protrusion inside combustion bowl. The target pressure ratio was achieved by suitable selection of turbocharger from simulation. Start of injection of 8 deg before TDC was found best for NOx vs PM tradeoff based on experiments. The optimum configuration was found best meeting the BS III CEV emissions with a reduction of 52% NOx and 72% PM without much compromise on fuel economy in operating duty cycle.