Study on low temperature heat release of partially premixed combustion in a heavy duty engine for real-time applications

Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature heat release (LTHR) is an important process to be investigated. A novel motoring pressure prediction algorithm based on variable polytropic exponents was introduced and utilized to estimate average heat transfer coefficient as well as heat dissipation for real-time applications. A series of parameters, such as start of combustion (SOC) of LTHR, crank angle of 50% heat released (CA50) during LTHR, duration of LTHR and heat amount of LTHR, were further analyzed under different engine operation conditions. The results demonstrated that: (1) the absolute motoring pressure prediction error was below 0.5 bar with a relative error below 4%; (2) the average heat released during LTHR was about 40–65 J, and the mass burned was about 1–3% of the total mass burned; (3) CA50 of LTHR was more stable than SOC of LTHR, and was a better indicator for real-time combustion phase control; (4) similar combustion phase and heat amount of LTHR could be reached by adjusting the timing of the third injection regardless the difference in timing of the second injection; (5) the combustion phase and heat amount of LTHR could be controlled by the duration of the second injection