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1、天津職業(yè)技術師范大學 2012 屆本科生畢業(yè)設計1General comments of automobile engine Engine is the source of automotive.so far, automotive engines are all powered by heat except for a few of automotives drived by electricity.modern automotive

2、 engines are called internal combustion engines because fuel burns inside the engine .The engine converts the burning fuel’s thermal energy to mechanical energy.By Cooling Systems Liquid-cooled engines and air-cooled

3、engines are being used .Liquid-cooled engines are the most common in the diesel industry .By Fuel System Gasoline diesel and propane fuel systems are currently used in a wide variety of engines .By Ignition Method Gas

4、engines use the spark (electrical)ignition diesel engines use the heat fro BDC to TDC ;it varies with cylinder bore size ,length of piston stroke ,and numb system injection .The calory of diesel engine come from the fuel

5、 emblazed by the compressed air.The diesel engine’compression ration is much bigger than the gas engine.Its sufficient calory is from the fuel burned by the pressed air.By valve Arrangement Four types of valve arrange

6、ments have been used in gasoline and diesel engines .Of the four types (L, T ,F ,and I heads ),the I head is commonly used on diesel engines .By Cylinder Arrangement Engine block configuration or cylinder arrangement

7、depends on cylinder block design .Cylinders may be arranged in a straight line one behind the other .The most common in-line designs are the four-and six-cylinder engines .The V type of cylinder arrangement uses two bank

8、s of cylinders arranged in a 60°to 90°V design .The most common examples are those with two banks of three to eight cylinders each .The opposed engine uses two banks of cylinders opposite each other with the cr

9、ankshaft in between .Engine’classificationAccording to the differences of the piston’movement, the piston intenal combusition engine will be classified reciprocating intenal combusition engine and rotary piston intenal c

10、ombusition engine.Then we will introduce working principle diagram of reciprocating internal combustion engine.Except for the wankel rotary ,engine ,all production automotive engines are the reciprocating ,or piston ,des

11、ign . Reciprocating means “up and down “ or “back and forth 天津職業(yè)技術師范大學 2012 屆本科生畢業(yè)設計3them in an enclosed cylinder at a controlled rate .A movable piston in the cylinder is forced down by the expanding gases of combustion

12、 .The movable piston in cylinder is connected to the top of a connecting rod .The bottom of the connected rod is attached to the offset portion is transferred to the crankshaft ,As the piston is forced down ,this offset

13、portion of a crankshaft ,to rotate .The reciprocating (back and forth or up and down )movement of the piston is converted to rotary (turning )motion of the crankshaft ,which supplies the power to drive the vehicle .In ge

14、neral an average air-fuel ratio for good combustion is about 15parts of air to 1 part of fuel by weight .However ,the diesel engine always takes in a full charge of air (since there is no throttle plate in most systems )

15、 ,but only a small part of this air is used at low or idle engine speeds .Air consists of about 20 percent oxygen while the remaining 80 percent is mostly nitrogen .This means that ,for every gallon of fuel burned ,the o

16、xygen in 9,000 to 10,000gallons of air is required .Four-Stroke CycleGasoline by itself will not burn ,it must be mixed with oxygen (air ) .This burning is called combustion and is a way of releasing the energy stored in

17、 the air-fuel mixture .To do any useful work in an engine ,the air-fuel mixture must be compressed and burned in a sealed chamber .Here the combustion energy can work on the movable piston to produce mechanical energy .T

18、he combustion chamber must be sealed as tightly as possible for efficient engine operation .Any leakage from the combustion chamber allows part of the combustion energy to dissipate without adding to the mechanical energ

19、y developed by the piston movement .The 4-stroke engine is also called the Otto cycle engine ,in honor of the German engineer ,Dr. Nikolaus Otto ,who first applied the principle in 1876 .In the 4-stroke engine ,four stro

20、kes of the piston in the cylinder are required to complete one full operating cycle :two strokes up and two strokes down .Each stroke is named after the action it performs-intake ,compression ,power ,and exhaust :1、Intak

21、e Stroke As the piston moves down ,the vaporized ,mixture of fuel ;and air enters the cylinder past the open intake valve .2、Compression Stroke The piston returns up ,the intake valve closes ,the mixture is compressed