【文章內(nèi)容簡介】 o the brake power rises MBT is reached, the brake torque drops, which slow down brake power, and eventually turn it down when peak power is )Curve of bsfc In low engine speed range, ηi increase while ηm decrease with increasing engine speed, be decrease in high engine speed range, bothηi and ηm decrease with increasing engine speed, thus be increases Speed characteristics of CI engines With the fuel control mechanism(rack or rod)fixed, the variation relations between engine main performance parameters such as brake torque, brake power and bsfc with engine speed is referred to speed characteristics of CI )Curve of brake torque In diesel engine, the torque produced under certain engine speed is mainlyhvVsr0hmQ=determined by circle fuelinjection addition percycle Δb is:lL0So the cycle fuel injection Δb is: Db=hvVsr0lL0and the Ttq canbe turned into: T=K39。hhDbtq2imFrom the above equation, we can get that the main factors that influence brake torque are ηi , ηm and Δb.(1)Indicated efficiency ηi peaks at a middle speed().In the low engine speed range,the loss due to heat transfer is large,so ηi is in high engine speeds range,reduced volumetric efficiency and increased Δb form richer mixture,resulting in the drop of indicated efficiency.(2)Mechanical efficiency ηm decreases with increasing engine speed().When engine speeds up,increases in mechanical loss,accessoriesconsumption and pumping loss decrease the mechanical efficiency.(3)Fuel injection percycle Δb increases with increasing engine speed due to the throttle effect in injector )Curve of brake power With increasing engine speed, the brake torque increases, so the brake power rises MBT is reached, the brake torque drops, which slow down the increase of brake )Curve of bsfc In low engine speed range, ηi increase while ηm decrease with increasing engine speed, be decrease in high engine speed range, bothηi and ηm decrease with increasing engine speed, thus be increases Comparison of SI engine speed characteristics with CI engine Differences between the two are the followings:(1)The torque curves of SI engine under all load range is relatively flat, while that of a SI engine drops drastically in high engine speed range.(2)The peak power can be reached in SI engine fullload power curve, ordinarily it is the rated power, while the peak point can hardly be reached in CI engine power curve.(3)The bsfc curves of CI engine under all load range is relatively flat, while that of a SI engine is more warping, especially in lowload 4 Diesel engine governing characteristicsA device for automatically controlling the speed of an engine by regulating the intake or injection of fuel, so that the engine speed is maintained at the desired level under all conditions of loading, is termed the injector speedregulating handle fixed and governor functioning, the variation relations of main performance parameters Pe, Ttq and be of diesel engine with engine speed is referred to as governing styles are used to illustrate governing characteristic：(1)load characteristic style(2)speed characteristic style Engine speed governors can be classed as speedlimiting, constantspeed or allspeed type by function。or classified as mechanical, electronics, pneumatic and hydraulic type by structure.(1)Construction machinery and tractors are normlly equipped with constantspeed governor.(2)Automobile used engines are usually fitted with speedlimiting 5 Engine universal characteristics One mon way to present the operating characteristics of an engine over its full load and speed range is to plot brake specific fuel consumption contours on a graph of brake mean effective pressure versus engine bmep occurs in the midspeed range。the minimum bsfc island is located at a slightly lower speed and at part map characteristics can be understood in terms of variations in ηi , ηm , ηv and the importance of heat losses and friction performance map can be plotted by two methods: by speed characteristics or load of universal characteristicsFirstly, bsfc be of SI engine is higher than that of CI engine；Secondly, the most economic region of SI engine located at the location of the upper, that is to say, high load the decrease of load, bsfc increases for CI engine, the most economic regions are more change load, the economic characteristic changes vehicle gasoline engine usually run at lower load, bsfc is high, economic characteristic is not vehicle diesel engine, because more condition are used in truck, engineering machinery, mining vehicles, loads are high, the economic characteristic are better from universal characteristics the universal characteristic figure, specific fuel consumption curve at the innermost is equal to the most economic area that engine is running, the outward the contour curve, the worse economic and location of equivalence bsfc curve have important influence on actualeconomic the shape of curve is longer at horizontal direction, it shows that bsfc changes little when engine runs at loan changes little and speed changes the shape of curve is longer at vertical direction, it shows that bsfc changes little when engine runs at loan changes great and speed changes cars with internal bustion engine, the most economic region should be roughly in the intermediate position of the universal characteristics, so mon speed and load can fall in the economic area, and specific fuel consumption curves in the transverse is longer than the tractor and engineering machinery with internal bustion engine, the speed range is smaller and the load range is larger, the most economic region should be near the calibration speed, and a longer along the longitudinal.第三篇：發(fā)動機原理—教案【發(fā)動機原理】教案教材: 《汽車發(fā)動機原理》張志沛 主編大連海運學院出版社長安大學汽車學院機電與動力研究所目 錄緒 論第一章 發(fā)動機工作循環(huán)及性能指標167。11 發(fā)動機理想循環(huán)概述5167。12 發(fā)動機實際循環(huán)熱量這部分熱量雖然在膨脹過程中還可能會釋放出來，但由于活塞已接近下止點，做功效果變差，熱效率下降。二 傳熱、流動損失（一）傳熱損失理論上: 壓縮、膨脹過程為絕熱過程。實際上: 大量熱量通過汽缸壁傳給冷卻水或空氣。傳熱損失是發(fā)動機中的最大損失，占總損失量的30%以上。因此，許多研究者致力于開發(fā)絕熱發(fā)動機。（二）流動損失理論上: 閉口系統(tǒng)，沒有氣體流動損失。