煤制油/碳酸二甲酯双燃料发动机排放特性研究

Emission Characteristics of Coal-to-Liquid/Dimethyl Carbonate Dual-Fuel Engine

摘要

煤制油可作为传统石油燃料的替代品，在发动机上使用能够更好地保障国家能源安全，同时推动煤炭的高效清洁利用. 通过发动机台架试验，探讨了不同负荷下煤制油掺混碳酸二甲酯对排放特性的影响. 结果表明：增加碳酸二甲酯混合比例，混合燃料着火时刻提前，燃烧效率上升. 其中，在中低负荷下，添加碳酸二甲酯对燃烧效率的提升相较于高负荷下更加显著. 在煤制油中掺混30%的碳酸二甲酯，CO排放最高降低50.9% ，为0.108 g/(kW·h)；烟度最低值为0.015 FSN，与煤制油相比降低 78.3%；NO_x 排放增加. 颗粒物排放数量浓度随着碳酸二甲酯掺混比例增加显著降低. 其中，积聚态颗粒(100～1 000 nm)数量浓度降幅最大，核态颗粒(23～100 nm)次之，超细颗粒(0～23 nm)降幅最小. 在 20%负荷工况下 3 种颗粒物下降最为明显，超细颗粒、核态颗粒和积聚态颗粒的降幅分别为70.1%、54.6%和43.9%. 颗粒物几何平均直径随碳酸二甲酯混合比例的上升而下降. 当发动机处于更高负荷工况下，燃料着火更早，燃烧效率上升；CO、THC排放和烟度下降，其中3种混合燃料的烟度分别下降31.3%、42.9%和46.4%；NO_x 排放增加；总排放颗粒数浓度降低，但 3 种颗粒物所占比例没有明显变化，几何平均直径呈现小幅增加. 在20%～60%负荷工况下，碳酸二甲酯的添加具有明显的颗粒数浓度和NO_x 权衡关系. 相较于负荷改变，碳酸二甲酯混合比例对减少颗粒物生成的效果更为显著.

Abstract

Coal-to-liquid(CTL)fuels can be used as alternatives to conventional petroleum-based fuels，enhancing national energy security and promoting the efficient and clean utilization of coal in engines. Engine bench tests were conducted to investigate the effects of dimethyl carbonate(DMC)blending in CTL on the emission characteristics using different loads. The results reveal that increasing the DMC blending ratio advances the ignition timing and enhances combustion efficiency. This enhancement is more significant at low and medium loadings than at high loads. Further，blending 30% DMC into CTL yields a maximum carbon monoxide(CO)emission reduction of 50.9%，reaching 0.108 g/(kW·h). The lowest soot is 0.015 FSN，representing a 78.3% reduction compared with CTL. However，increased N_x emissions are observed. Additionally，the particle number concentration considerably decreases with higher DMC blending ratios. The accumulation-mode particles(100—1 000 nm)exhibit the highest reduction，followed by nucleation-mode particles(23—100 nm). Notably，the ultrafine particles(0—23 nm)exhibit the smallest decrease. At a 20% load，the most significant reductions in the three particle size groups are observed，with the decrease of the ultrafine，nucleation-mode，and accumulation-mode particles being 70.1%，54.6%，and 43.9%，respectively. The geometric mean diameter of the particles decreases with the increasing DMC blending ratio. At higher engine loads，the fuel ignites faster，with enhanced combustion efficiency. Additionally，the CO，tetrahydrocannabinol(THC)，and soot emissions decreases，with the soots of the three mixed fuels decreasing by 31.3%，42.9%，and 46.4%，respectively. Further，the NO_x emissions increase while the total particle number concentration decreases，although the proportions of the three particles do not change substantially，and the geometric mean diameter increases slightly. A clear trade-off relationship is observed between the particle number concentration and NO_x emissions at loads of 20%—60%. Compared with load variations，the DMC blending ratio exerts a more significant effect on the suppression of particle formation.

关键词

煤制油 / 碳酸二甲酯 / 柴油机 / 排放特性

Key words

coal-to-liquid(CTL) / dimethyl carbonate(DMC) / diesel engine / emission characteristics

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基金资助

广西省科技重大专项资助项目(桂科 AA23062090)

广西省科技重大专项资助项目(桂科 AA23062012)

国家自然科学基金资助项目(52366007)