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首页> 外文会议>Homogeneous charge compression ignition engines, 2009 >Influence of EGR Quality and Unmixedness on the High-Load Limits of HCCI Engines
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Influence of EGR Quality and Unmixedness on the High-Load Limits of HCCI Engines

机译：EGR质量和混合气对HCCI发动机高负荷极限的影响

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This work explores how the high-load limits of HCCI are affected by fuel autoignition reactivity, EGR quality/composition, and EGR unmixedness for naturally aspirated conditions. This is done for PRF80 and PRF60. The experiments were conducted in a single-cylinder HCCI research engine (0.98 liters) with a CR = 14 piston installed. By operating at successively higher engine loads, five load-limiting factors were identified for these fuels: 1) Residual-NO_x-induced run-away advancement of the combustion phasing, 2) EGR-NO_x-induced run-away, 3) EGR-NO_x/wall-heating induced run-away 4) EGR-induced oxygen deprivation, and 5) excessive partial-bum occurrence due to EGR unmixedness. The actual load-limiting factor is dependent on the autoignition reactivity of the fuel, the EGR quality level (where high quality refers to the absence of trace species like NO, HC and CO, i.e. simulated EGR), the level of EGR unmixedness, and the selected pressure-rise rate (PRR). For a reactive fuel like PRF60, large amounts of EGR are required to control the combustion phasing. Therefore, for operation with simulated EGR, the maximum IMEP becomes limited by the available oxygen. When real EGR (with trace species) is used instead of the simulated EGR, the maximum IMEP becomes limited by EGR-NO_x/wall-heating induced runaway. For the moderately reactive PRF80 operated with simulated EGR, the maximum IMEP becomes limited by residual-NO_x-induced run-away. Furthermore, operation with real EGR lowers the maximum steady IMEP because of EGR-NO_x-induced run-away. This is similar to PRF60. Finally, the data show that EGR/fresh-gas unmixedness can lead to a substantial reduction of the maximum stable IMEP for operation with a low PRR. This happens because the EGR unmixedness causes occasional partial-burn cycles due to excessive combustion-phasing retard for cycles that induct substantially higher-thanaverage level of EGR gases.
机译：这项工作探索了在自然吸气条件下，燃料自燃反应性，EGR质量/组成和EGR不混合如何影响HCCI的高负荷极限。这是针对PRF80和PRF60完成的。实验是在装有CR = 14活塞的单缸HCCI研究发动机（0.98升）中进行的。通过在更高的发动机负荷下连续运行，为这些燃料确定了五个负荷限制因素：1）残余NO_x引起的燃烧阶段失控提前； 2）EGR-NO_x引起的燃烧失控； 3）EGR- NO_x /壁加热引起的失控4）EGR引起的氧气剥夺，以及5）由于EGR混合不充分而引起的部分燃烧。实际的负载限制因素取决于燃料的自燃反应性，EGR质量等级（其中高质量是指不存在诸如NO，HC和CO等微量物质，即模拟EGR），EGR混合度不高以及选定的压力上升率（PRR）。对于像PRF60这样的反应性燃料，需要大量的EGR以控制燃烧阶段。因此，对于使用模拟EGR的运行，最大IMEP受到可用氧气的限制。当使用实际EGR（具有痕量物质）代替模拟EGR时，最大IMEP受到EGR-NO_x /壁加热引起的失控的限制。对于使用模拟EGR运行的中度反应性PRF80，最大IMEP受到残留NO_x引起的失控的限制。此外，由于EGR-NO_x引起的失控，实际EGR的运行会降低最大稳定IMEP。这类似于PRF60。最后，数据表明，对于低PRR的运行，EGR /新鲜气体的不混合会导致最大稳定IMEP的显着降低。发生这种情况是因为EGR的不混合会导致偶尔的部分燃烧循环，这是由于引入了明显高于平均水平的EGR气体的循环的燃烧相位延迟过大所致。

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