低压天然气喷射的船用二冲程低速双燃料发动机爆震研究

Knock of Low-Speed Two-Stroke Marine Dual-Fuel Engine with Low Injection Pressure of Natural Gas

关键词:  低速柴油-天然气双燃料发动机  预混合燃烧  涡流  爆震  三维CFD数值模拟  废气再循环

Key words:  Low-speed diesel-natural gas dual-fuel engine  Premixed combustion  Swirl  Knock  3D CFD numerical simulation  Exhaust gas recirculation

摘要:

为了解决大缸径船用预混天然气双燃料发动机的爆震问题，并拓展天然气的稀燃边界，基于三维数值模拟的方法对大缸径船机进行了仿真模拟。分析了大缸径双燃料发动机爆震的特点，并对缸内涡流强度和废气再循环（EGR）率对爆震的影响进行了研究。研究结果表明：大缸径预混天然气发动机的爆震位置往往发生在气缸边缘，火焰面的传播过程是引起缸内爆震的主要因素。随着缸内涡流从无到有的增强，缸内的爆震强度随之增强；当涡流到达一定程度后，随着涡流的增强，缸内的爆震强度反而降低；缸内加入EGR可以提高天然气当量比的同时减少爆震的强度，可以拓展天然气的稀燃边界。

Abstract:

In order to solve the knock problem of large-bore marine dual-fuel engines with premixed natural gas and expand the lean burn boundary of natural gas，based on the engine’s three-dimensional numerical simulation， the knock characteristics in the large-bore dual-fuel engine were analyzed， and the effects of swirl intensity in-cylinder and EGR （Exhaust Gas Recirculation） rate on knock were studied. The results show that the knock positions of large-bore premixed natural gas engines often occur at the edge of cylinder. The propagation process of flame surface is the main factor causing the knock in-cylinder. The knock intensity increases with the increase of the swirl intensity in the cylinder. When the swirl intensity reaches a certain value， the knock intensity decreases with the increase of the swirl intensity. Adding EGR in the cylinder can increase the equivalence ratio of natural gas but reduce the knock intensity at the same time， additionally it can expand the lean burn boundary of natural gas.