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1、目录Miller cycle1Overview1Miller cycle engine from Mazda3Miller cycleIn engineering, the Miller cycle is a combustion process used in a type of four-stroke internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, in the 1940s.OverviewThis type of engine was firs
2、t used in ships and stationary power-generating plants, but was adapted by Mazda for their KJ-ZEM V6, used in the Millenia sedan, and in their Eunos 800 sedan (Australia) luxury cars. More recently, Subaru has combined a Miller cycle flat-4 with a hybrid driveline for their concept Turbo Parallel Hy
3、brid car, known as the Subaru B5-TPH.A traditional Otto cycle engine uses four strokes, of which two can be considered high power the compression stroke (high power consumption) and power stroke (high power production). Much of the internal power loss of an engine is due to the energy needed to comp
4、ress the charge during the compression stroke, so systems that reduce this power consumption can lead to greater efficiency.In the Miller cycle, the intake valve is left open longer than it would be in an Otto cycle engine. In effect, the compression stroke is two discrete cycles: the initial portio
5、n when the intake valve is open and final portion when the intake valve is closed. This two-stage intake stroke creates the so called fifth stroke that the Miller cycle introduces. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled
6、 back out the still-open intake valve. Typically this loss of charge air would result in a loss of power. However, in the Miller cycle, this is compensated for by the use of a supercharger. The supercharger typically will need to be of the positive displacement (Roots or Screw) type due to its abili
7、ty to produce boost at relatively low engine speeds. Otherwise, low-rpm torque will suffer.A key aspect of the Miller cycle is that the compression stroke actually starts only after the piston has pushed out this extra charge and the intake valve closes. This happens at around 20% to 30% into the co
8、mpression stroke. In other words, the actual compression occurs in the latter 70% to 80% of the compression stroke.In a typical spark ignition engine, the Miller cycle yields an additional benefit. The intake air is first compressed by the supercharger and then cooled by an intercooler. This lower i
9、ntake charge temperature, combined with the lower compression of the intake stroke, yields a lower final charge temperature than would be obtained by simply increasing the compression of the piston. This allows ignition timing to be advanced beyond what is normally allowed before the onset of detona
10、tion, thus increasing the overall efficiency still further.An additional advantage of the lower final charge temperature is that the emission of NOx in diesel engines is decreased, which is an important design parameter in large diesel engines on board ships and power plants.Efficiency is increased
11、by raising the compression ratio. In a typical gasoline engine, the compression ratio is limited due to self-ignition (detonation) of the compressed, and therefore hot, air/fuel mixture. Due to the reduced compression stroke of a Miller cycle engine, a higher overall cylinder pressure (supercharger
12、pressure plus mechanical compression) is possible, and therefore a Miller cycle engine has better efficiency.The benefits of utilizing positive displacement superchargers come with a cost. 15% to 20% of the power generated by a supercharged engine is usually required to do the work of driving the su
13、percharger, which compresses the intake charge (also known as boost).A similar delayed-valve closing method is used in some modern versions of Atkinson cycle engines, but without the supercharging. These engines are generally found on hybrid electric vehicles, where efficiency is the goal, and the p
14、ower lost compared to the Miller cycle is made up through the use of electric motors.另：备息而言之,Miller-cycle引擎有下列特黑占：1. 利用延MM正畤来降低”有效厘编比(由10:1-8:1)舆活塞揖失pumping-loss(能段省 油的原因)2. 用雨彳固intercooler来冷WMM的空M!(能减少暴振的畿生.ect)3吨一步降低燃燎废的氧化物排放檬塑(如:NOx,CO2.etc)各卓蔽的新引擎都有逼檬的趟勃4.利用Lysholm檄械增厘器来完成行程，业芍射罩弓鱼而有力的性能!(高焉力舆扭力
15、的主因)Miller cycle engine from MazdaWhat is the Miller cycle?The key to improving fuel efficiency lies in raising an engines thermal efficiency. This can be done by increasing the expansion ratio. The expansion ratio is the amount of work the engine does each time the air-fuel mixture in the cylinders
16、 detonates. However, in conventional engines the expansion ratio is the same as the compression ratio, so increasing the expansion ratio will also raise the compression ratio. This is a problem because a high compression ratio causes abnormal combustion, or knocking.In most engines compression ratio = expansion ratioIQ : 1compresslion strokeE.Kpanon raftta : Tiie ratio of tiieorf the iwnarted fud before an
