要稳定提高卡车和小型工业柴油机的额定输出功率,很大程度上依赖涡轮增压器增压压力提高,但增压压力是不容易进一步提高的。首先,在增加发动机最大输出功率时,要获得低负荷和低转速下的足够扭矩储备就更加困难,相反还要影响驱动性和排放。其次,一般用在小型发动机涡轮增压器中的单级离心压气机,正接近压力比的极限。这是使用低成本材料、并保持发动机转速变化范围内所要求的气流量所能达到的极限值。位于英格兰Haddeisfield的Holset工程有限公司正在发展涡轮增压器的设计,来克服这两方面的困难。当发动机处于低负荷和低转速时,废气中用于驱动涡轮的能量减少。这时涡轮一般不能提供压气机所需的能量,不能向发动机提供适当的空气。发 In order to steadily increase the rated output power of trucks and small industrial diesel engines, the turbocharger boost pressure is greatly relied on, but the boost pressure is not easily further increased. First of all, to increase the maximum output power of the engine, it is more difficult to obtain sufficient torque reserve at low load and low speed, on the contrary, the driving and emission are also affected. Second, single stage centrifugal compressors, which are commonly used in small engine turbochargers, are approaching the pressure ratio limit. This is the limit that can be achieved with low cost materials and with the required gas flow over a variable engine speed range. Holset Engineering Ltd. in Haddeisfield, England, is developing turbocharger designs to overcome both of these difficulties. When the engine is at low load and low speed, the energy used to drive the turbine in the exhaust gas is reduced. Turbines at this time generally do not provide the energy required by the compressor and can not provide the engine with adequate air. hair