Study on LTC for light duty engines - Part 2 - Spray enhancements

- Diffusion-flame zero-NOX and zero-soot combustion strategy.
- Reduction on equivalence ratio at the lift-off length decreased soot precursors.
- Very low O2% led to low temperature combustion avoiding NOX and soot formation.
- Enhancement of spray characteristics allowed more suitable combustion conditions.
- CO, IMEP and HC emissions reduction if compared to the previous study.

This paper presents the 2nd part of a study on low temperature diffusive combustion in a small HSDI (High Speed Direct Injection) engine with the objective of avoiding simultaneously NOX and soot formation, aiming to extend the range of operation conditions where this combustion strategy has been achieved and. Also, it was intended to reduce CO and HC emissions, considered very high in the 1st part of the tests. New hardware configuration was chosen in order to improve air entrainment in the lift-off length such as increasing injection pressure, reducing fuel injection rate and nozzle hole diameter. Also, a parametric study on the behavior of in-cylinder air thermodynamic characteristics towards the diffusion-flame low temperature combustion was also carried out in order to evaluate the important aspects of each one and observe how the LTC range has been extended.The strategy is based mainly in a significant reduction of the equivalence ratio at the lift-off length cross section and the combustion temperature, maintaining the conventional mixing controlled diesel jet structure. In this 2nd part of the study, injection pressure was increased and new nozzles with reduced holes were used to enhance air entrainment and the injection rate was reduced to extend the duration of diffusion-flame combustion phase.The new proposal allowed extending Diffusion-flame LTC range, being possible to achieve this combustion modality with higher air temperature which lead to considerable reduction in HC, CO and combustion noise while NOx and Soot remained insignificant.