Experimental Study on Low Temperature Cold Start and Low Load of Passive Pre-chamber Engine
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摘要: 预燃室射流点火是改善汽油发动机热效率的有效手段，为了研究和改善被动预燃室低温冷起动及低负荷时的燃烧稳定性，设计了不同容积、孔面积、材料、喷孔结构的被动预燃室装置，安装在一台涡轮增压汽油发动机上，进行了低温冷起动试验，以及低速、低负荷燃烧稳定性试验。研究结果表明，被动预燃室容积、孔面积、材料、喷孔结构对低温冷起动性能有显著影响。预燃室容积较小时，预燃室内部淬熄层占预燃室容积的比例大，预燃室内部混合气少。较小的孔径或孔面积减少了预燃室内残余废气的排出。旋转孔使得预燃室内部废气分层，火花塞附近废气比例大。较高的导热率使预燃室冷起动时预燃室散热较快。因此，小容积、小孔径、高导热率材料以及旋转喷孔等均不利于发动机冷起动。优化结构的被动预燃室在-20 ℃~-8 ℃的冷起动工况下能实现发动机稳定着火起动。点火角和排气VVT对发动机的燃烧稳定性影响较小。进气VVT对预燃室燃烧稳定性影响较大，进气门开起时刻推迟，着火上止点附近缸内湍动能变强；另一方面实际压缩比变大，主燃烧压入预燃室内部的新鲜混合气比例提高，预燃室点火燃烧稳定性显著改善。Abstract: Passive pre-chamber jet ignition is an effective means to improve the thermal efficiency of gasoline engines. In order to study and improve the passive pre-chamber combustion stability at the low-temperature cold start and low-load, several passive pre-chambers with different volume, orifice area, material, and orifice structure was designed and installed on a turbocharged gasoline engine. Low temperature cold start test, low speed and low load combustion stability test were carried out. The results show that the passive pre-chamber volume, the orifice area, the material and the orifice structure have significant effects on the cold start performance. When the volume of the pre-chamber is small, the proportion of quenching layer in the pre-chamber volume is large, and the mixture in the pre-chamber is small. The smaller orifice or orifice area increases the residual exhaust gas in the pre-chamber. The rotating orifice makes the exhaust gas in the pre-chamber stratified, and the proportion of exhaust gas near the spark plug is large. The high thermal conductivity material makes the pre-chamber heat dissipation faster during cold start. Therefore, small volume, small orifice, high thermal conductivity and rotating orifice are not conducive to the cold start of the engine. The optimized structure of the passive pre-combustion chamber can realize the stable cold start at -20 ℃ to -8 ℃. Ignition timing and exhaust VVT have little effect on the combustion stability of the engine. The intake VVT has a great influence on the combustion stability of the pre-chamber. The opening of the intake valve is delayed, and the turbulent kinetic energy in the cylinder becomes stronger near the top dead center. On the other hand, the actual compression ratio of the engine becomes larger, the proportion of the fresh air-fuel mixture pressed into the pre-chamber is increased, and the combustion stability of the pre-chamber is significantly improved.
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Key words:
- passive pre-chamber /
- low temperature /
- cold start /
- low speed /
- low load
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表 1 发动机主要结构参数
参数 数值 缸径/mm 74 冲程/mm 87 排量/L 1.496 压缩比 11.3 缸数 4 额定转速/(r·min-1) 6 000 额定功率/kW 120 喷油方式 35 MPa缸内直喷系统 燃烧室结构 缸盖蓬顶型+活塞顶浅坑型燃烧室 进气方式 废气涡轮增压 
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表 2 试验预燃室参数
参数 方案 1 2 3 4 5 容积/mL 0.73 0.73 0.73 0.73 0.35 孔径/mm 1.2 1.2 0.8 1.2 1.2 孔数/个 6 6 6 6 6 孔面积/mm2 6.78 6.78 3.1 6.78 6.78 孔角度/(°) 0 30 0 0 0 材料 304不锈钢 304不锈钢 304不锈钢 H62黄铜 铬锆铜
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表 3 不同温度下不同预燃室方案的冷起动情况
名称 方案 1 2 3 4 5 热机状态+加浓 √ × √ √ × -8 ℃ 启动过程(前8 s) 原机状态λmin=0.75 × × × × × 加浓λmin=0.71 √ × × √ × 进一步加浓λmin=0.68 - × √ - × 怠速 √ × √ √ × -12 ℃ 启动过程(前8 s) 原机状态λmin=0.73 × × × × × 加浓λmin=0.69 × × × × × 进一步加浓λmin=0.66 √ × √ √ × 怠速 √ × × × × -20 ℃ 启动过程(前8 s) 原机状态λmin=0.70 × × - - - 加浓λmin=0.67 √ × - - - 进一步加浓λmin=0.64 - × - - - 怠速 √ × - - - 注：√代表能稳定燃烧；×代表不能稳定点火燃烧；-代表未做试验。
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