重载低压缩比发动机二冲程制动性能模拟研究

Simulation Research on Two-Stroke Braking Performance of Heavy-Duty Low Compression-Ratio Engine

采用数值模拟的方法研究了不同制动模式、压缩比、海拔高度等对制动性能的影响。结果表明:压缩比的降低和海拔高度的增加均导致发动机制动功率大幅度降低。提高压缩比和采用二冲程制动模式是提高低压缩比发动机制动功率的有效措施。压缩比为11.6时,与四冲程制动模式相比,二冲程制动模式产生的制动功率可提升69.6%~80.5%,最大缸压低于6.0 MPa的限值,并且其可运行转速范围不受涡轮增压器危险区的限制。当前应用领域中,高压缩比(17.0)发动机上采用四冲程制动模式获得的制动功率最高。由于短期内难以提高低压缩比发动机的压缩比,仅通过在低压缩比(11.6)发动机上采用二冲程制动模式仍可将制动功率提高17.5%~30.4%,最大缸压降低25.2%~29.3%。故在应用天然气机等低压缩比发动机的中重型载货汽车上推荐采用二冲程制动模式,这将大幅度提高车辆制动安全性。

The effects of different braking modes,compression ratios and altitudes on braking performance were studied by numerical simulation.The results show that the reduction of compression ratio and the increase of altitude can greatly reduce the engine braking power.Increasing the compression ratio and adopting two-stroke braking mode are effective in improving the braking power of low compression-ratio engines.Compared with four-stroke braking mode,the braking power of two-stroke braking mode with the compression ratio of 11.6 can increase by 69.6%~80.5%,the maximum cylinder pressure is lower than the limit of 6.0 MPa,and its operating speed range is not limited by the turbocharger’s danger zone.The application of four-stroke compression release braking mode on a high compression-ratio(17.0)engine has the highest braking power in the current application field.Since it is difficult to increase the compression ratio in a short term,only the application of two-stroke braking mode on a low compression-ratio(11.6)engine can still increase the braking power by 17.5%~30.4%and reduce the maximum cylinder pressure by 25.2%~29.3%.Therefore,two-stroke braking mode is recommended for medium and heavy trucks with low compression-ratio engines such as natural gas engines,which will greatly improve the vehicle braking safety.