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A novel strategy of extremely delayed intake valve opening to improve the cold-start characteristics of a low compression ratio diesel engine
International Journal of Engine Research ( IF 2.5 ) Pub Date : 2021-07-26 , DOI: 10.1177/14680874211034691
V Vikraman 1 , K Anand 1 , A Ramesh 1
Affiliation  

Combined in-cylinder and after-treatment emission control methods are generally adopted to meet the current stringent emission targets for diesel engines. It is well established that reducing the geometric compression ratio (CR) results in a simultaneous reduction in the oxides of nitrogen (NOx) and soot emissions in diesel engines. However, poor cold-start characteristics prevent extensive use of low compression ratio (LCR) diesel engines for automotive applications. In the present work, a novel extremely delayed intake valve opening (IVO) strategy is proposed to improve the cold-start characteristics of a light-duty LCR diesel engine. A commercial one-dimensional gas-exchange model was used to optimize the intake valve open and close timings. The results corresponding to a cranking speed of 200 rpm and ambient temperature of 0°C show that advancing the intake valve close (IVC) timing increases the effective compression stroke that can improve the cylinder temperature by 5%. Further, implementing ‘extremely delayed IVO’ by retarding the timing from 1°CA to 61°CA aTDC could help to further increase the cylinder temperature by 14% compared to the base timings. The delayed opening of the intake valve leads to a higher expansion of the cylinder mass, leading to a lower cylinder pressure before IVO and a higher intake air velocity immediately after IVO. With the higher intake air velocity, the incoming air’s kinetic energy is dissipated to increase the stagnation temperature, resulting in an overall benefit in cylinder temperature. The experimental measurements conducted in a cold chamber with the optimized IVO and IVC timings confirmed the benefits by achieving a better cold-startability of the LCR engine. In comparison, the LCR engine with the stock valve timings could be started only up to +5°C, the optimized valve timings could ensure startability up to −10°C without any starting aids. Thus, the proposed approach of adopting the optimized valve timings can help LCR diesel engines to overcome the limitations of cold-startability.



中文翻译:

一种改善低压缩比柴油机冷启动特性的极延迟进气门开启新策略

通常采用缸内和后处理相结合的排放控制方法来满足目前柴油发动机严格的排放目标。众所周知,降低几何压缩比 (CR) 会同时减少氮氧化物 (NO x) 和柴油发动机的碳烟排放。然而,较差的冷启动特性阻碍了低压缩比 (LCR) 柴油发动机在汽车应用中的广泛使用。在目前的工作中,提出了一种新颖的极延迟进气门开启 (IVO) 策略来改善轻型 LCR 柴油发动机的冷启动特性。使用商业一维气体交换模型来优化进气门打开和关闭正时。对应于 200 rpm 的起动速度和 0°C 的环境温度的结果表明,提前进气门关闭 (IVC) 正时增加了有效压缩冲程,可以将气缸温度提高 5%。更远,通过将正时从 1°CA 延迟到 61°CA 来实现“极度延迟的 IVO”,与基本正时相比,aTDC 有助于将气缸温度进一步提高 14%。进气门的延迟打开导致气缸质量的更大膨胀,从而导致 IVO 之前的气缸压力较低,而 IVO 之后的进气速度较高。进气速度越高,进气的动能就会消散,从而提高滞止温度,从而使气缸温度整体受益。在具有优化的 IVO 和 IVC 正时的冷室中进行的实验测量证实了通过实现 LCR 发动机更好的冷启动性的好处。相比之下,带有备用气门正时的 LCR 发动机只能在高达 +5°C 的温度下启动,优化的气门正时可以确保在 -10°C 下的可启动性,无需任何启动辅助。因此,所提出的采用优化气门正时的方法可以帮助 LCR 柴油发动机克服冷启动性的限制。

更新日期:2021-07-27
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