Effects of Different Miller Cycles on Combustion and Performance of Biogas Engines
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摘要: 为了研究不同米勒循环对大功率沼气发动机在额定工况的燃烧和性能的影响, 基于一台1.15 MW增压型沼气发动机及其仿真模型, 通过变化进气门关闭正时, 将沼气发动机由奥托循环改为不同米勒循环。仿真研究结果表明: 在沼气发动机输出目标功率相同的情况下, 随着早米勒的提前和晚米勒的推后, 其缸内最大燃烧压力、最高燃烧温度、单缸排气温度、燃油消耗率及氮氧化物排放均降低明显, 这表明早米勒循环和晚米勒循环对沼气发动机的燃烧和性能提升有较好的效果; 随着早米勒的提前和晚米勒的推后, 为了保证输出相同的功率, 其增压压力需要提高, 但其充气效率明显下降; 随着晚米勒的加强, 进气门关闭时刻进气倒流现象明显, 容易出现进气回火现象, 早米勒在进气门关闭时刻未发生任何进气倒流现象; 相比晚米勒, 早米勒更好的适宜预混增压型沼气发动机进气混合需求; 所研究机型在ML-70时刻比原ML0时刻, 其优点是爆发压力、燃气消耗率、氮氧化物排放分别下降3.74 %、2.49 %、23.58 %, 达到了降低爆震、提高效率、减小排放的目标。Abstract: In order to study the effects of different miller cycles on the combustion and performance of a high-power biogas engine on different conditions, based on the 1.15 MW supercharged biogas engine and its simulation model, the Otto cycle of the biogas engine was changed into different miller cycles by changing the timing of inlet valve closing. Simulation results show that the biogas engine's power output reaches the same target, as the early miller cycle gets earlier and the late miller cycle gets later. The maximum combustion pressure, maximum combustion temperature in the cylinder, its exhaust temperature, fuel consumption rate and nitrogen oxide emissions are reduced obviously. This suggests that the early miller cycle and late miller cycle of the gas engine's combustion and performance are improved. With the advance of the early miller cycle and the delay of the late miller cycle, in order to ensure the same output power, their pressure needs to be increased, but the charging efficiency obviously decreases. With the strengthening of the late miller cycle, the inlet backflow phenomenon occurs when the intake valve is closed, and the inlet backflow phenomenon easily occurs. No inlet backflow phenomenon occurs when the intake valve of the early miller cycle is closed. Compared with the late miller cycle, the early miller cycle is more suitable for the intake mixture demand of a premixed and supercharged gas engine. The explosion pressure, gas consumption rate and nitrogen oxide emission of the miller cycle studied in this paper decrease by 3.74 %, 2.49 % and 23.58 % respectively, thus reducing its detonation and emissions and improving its efficiency.
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Key words:
- biogas engine /
- miller cycle /
- combustion /
- performance /
- emissions
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图 4 不同米勒循环下的缸内燃烧瞬态压力
Figure 4. Transient pressure of in-cylinder combustion under different Miller cycles
图 5 不同米勒循环下的最大缸内压力变化趋势
Figure 5. Variation trend of maximum in-cylinder pressure under different Miller cycles
图 6 不同米勒循环时刻缸内燃烧温度瞬态图
Figure 6. Diagram of transient combustion temperature in cylinder at different Miller cycle times
图 7 不同米勒循环时刻最大燃烧温度变化趋势
Figure 7. Variation trend of maximum combustion temperature at different Miller cycles
图 8 不同米勒循环时刻的累计放热率变化
Figure 8. Cumulative heat release rate changes at different Miller cycle times
图 9 不同米勒循环进气质量流量瞬态图
Figure 9. Diagram of transient inlet mass flow with different Miller cycles
图 10 不同米勒循环压缩终了温度变化趋势
Figure 10. Temperature change trend at the end of different Miller cycle compression
图 11 不同米勒循环充气效率变化趋势
Figure 11. Variation trend of charging efficiency of different Miller cycles
图 12 不同米勒循环增压压力变化趋势
Figure 12. Variation trend of booster pressure in different Miller cycles
图 13 不同米勒循环燃气消耗率变化趋势
Figure 13. Variation trend of gas consumption rate in different Miller cycles
图 14 不同米勒循环单缸排气温度变化趋势
Figure 14. Variation trend of single cylinder exhaust temperature in different Miller cycles
图 15 不同米勒循环氮氧化物的排放变化趋势
Figure 15. Variation trend of nitrogen oxide emissions in different Miller cycles
图 16 不同压缩比缸内燃烧瞬态压力
Figure 16. Transient pressure of combustion in cylinder at different compression ratios
图 17 不同压缩比缸内燃烧瞬态温度
Figure 17. Transient combustion temperature in cylinder at different compression ratios
图 18 不同压缩比单缸排温变化趋势
Figure 18. Variation trend of single cylinder exhaust temperature at different compression ratios
图 19 不同压缩比氮氧化物变化趋势
Figure 19. Variation trend of nitrogen oxides at different compression ratios
图 20 不同压缩比燃气消耗率变化趋势
Figure 20. Variation trend of gas consumption at different compression ratios
表 1 实验数据与仿真结果误差率
Table 1. Error rate between experimental data and simulation results
参数 实验数据与仿真结果误差率/% 输出功率 0.51 最大缸内压力 2.23 最高燃烧温度 2.82 压气机后压力 1.85 压气机后温度 1.69 单缸排温 1.36 涡轮前总排温 2.17 涡轮前废气压力 2.36 
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表 2 ML-70与原ML0米勒循环仿真结果对比
Table 2. Comparison of simulation results between ML-70 and original ML0 Miller cycles
参数 ML0 ML-70 变化方向 变化率/% 最大爆发压力/bar 117.5 113.1 下降 3.74 最大燃烧温度/K 1954.0 1936.9 下降 0.87 充气效率 0.95 0.83 下降 12.75 增压压力/bar 2.65 2.92 增大 10.1 压缩终了温度/K 412.2 395.3 下降 4.11 燃气消耗率/[g·(kWh)-1] 172.9 168.6 下降 2.49 排气温度/K 870.1 842.4 下降 3.18 氮氧化物排放/ppm 267.8 204.7 下降 23.58
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表 3 ML-70-RC12.5与原ML0米勒循环仿真结果对比
Table 3. Comparison of simulation results between ML-70-RC12.5 and original ML0 Miller cycles
参数 ML0 ML-70-RC12.5 变化方向 变化率/% 最大爆发压力/bar 117.5 121.6 上升 3.46 最大燃烧温度/K 1 954 1 937.2 下降 0.86 充气效率 0.95 0.82 下降 13.1 增压压力/bar 2.65 2.90 增大 9.45 压缩终了温度/K 412.3 396.3 下降 3.86 燃气消耗率/[g·(kWh)-1] 172.9 166.8 下降 3.57 排气温度/K 870.0 829.3 下降 4.69 氮氧化物排放/ppm 267.82 234.14 下降 12.5
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