Thermal Efficiency Improvements with Split Primary Fuel Injections in Semi-Premixed Diesel Combustion with Multi-Peak Shaped Heat Release

Mechanism of thermal efficiency improvement in twin shaped semi-premixed diesel combustion

“…7 To overcome these disadvantages, there are several reports of the semi-premixed diesel combustion mode, with a firststage premixed combustion of the primary injection and a second-stage spray diffusive combustion of the secondary injection suppressing the rapid first-stage premixed combustion, realizing a wider IMEP range with overall milder combustion. [11][12][13][14][15][16][17][18][19][20][21][22] The CO and THC formed in the first-stage premixed combustion are oxidized with the second-stage spray combustion, resulting in the improvements in combustion efficiency. The authors have established efficient and clean semipremixed diesel combustion mode with systematic investigations of the effects of operating parameters including intake gas and fuel injection conditions on the combustion characteristics over a wide operating range.…”

“…The authors have established efficient and clean semipremixed diesel combustion mode with systematic investigations of the effects of operating parameters including intake gas and fuel injection conditions on the combustion characteristics over a wide operating range. [18][19][20] Optimizing the first-stage combustion fraction and the second injection timing to the position of the twin peak shape heat release, significant reductions in engine noise when compared with the premixed diesel combustion with a single injection were achieved, in addition to improved indicated thermal efficiency and decreased NOx emissions and without increases in other exhaust gas emissions, including the CO, THC, and smoke emissions. 18 A significantly high indicated thermal efficiency exceeding 50% is established with a reduction in the intake oxygen concentration due to the smaller cooling loss.…”

“…19 Both the heat flux value and the high heat flux area in the twin combustion are smaller than in the single premixed combustion due to decreases in the quantities of burned gas near the combustion chamber wall with the separated fuel injections, showing the mechanism of the reduction in cooling loss in the twin combustion. 20 In this report, the energy balances and the exhaust gas emissions in the optimized semi-premixed diesel combustion mode and in the typical conventional diffusive diesel combustion mode mainly with diffusive combustion were compared to show the superiority of the semi-premixed mode and the mechanisms of the thermal efficiency improvements were analyzed with 3-D CFD analysis. The heat release of the semi-premixed mode can be more concentrated at the top dead center, expecting to realize a significant reduction in the exhaust loss and a higher thermal efficiency than the conventional diffusive diesel combustion mode.…”

“…19 Both the heat flux value and the high heat flux area in the twin combustion are smaller than in the single premixed combustion due to decreases in the quantities of burned gas near the combustion chamber wall with the separated fuel injections, showing the mechanism of the reduction in cooling loss in the twin combustion. 20…”

Modeling of diesel spray tip penetration during start-of-injection transients

“…For the advanced combustion strategies that utilize the multiple-injection, [35][36][37][38] the fuel injection duration for a single pulse is significantly reduced to maintain the total injection quantity constant in one cycle, causing the SOI transients more significant in an injection event. Moreover, the continuously increased injection pressure in modern diesel engines 39,40 results in the shorter and shorter injection duration, making the SOI transients play a more important role in the whole injection processes.…”