In the four-stroke, reciprocating, internal combustion engine that powers most a

Question

In the four-stroke, reciprocating, internal combustion engine that powers most automobiles as well as most small general aviation aircraft, combustion of the fuel-air mixture lakes place in the volume between the top of the piston and the top of the cylinder. (Reciprocating engines are discussed in Chap. 9.) The gas mixture is ignited when the piston is essentially at the end of the compression stroke (called top dead center), when the gas is compressed to a relatively high pressure and is squeezed into the smallest volume that exists between the top of the piston and the top of the cylinder. Combustion takes place rapidly before the piston has much time to start down on the power stroke. Hence the volume of the gas during combustion stays constant; that is the combustion process is at constant volume. Consider the case where the gas density and temperature at the instant combustion starts are 11.3 kg/m3 and 625 K. respectively. At the end of the constant-volume combustion process, the gas temperature is 4000 K Calculate the gas pressure at the end of the constant-volume combustion. Assume that the specific gas constant for the fuel-air mixture is the same as that for pure air.

Explanation / Answer

only pressure at the end of constant volume process( p1t2=p2t1)

we have t1 and t2; we can find p1 from given values and only unknown is p2 , which can be found out by above formula...

PV=nRT;

PV=m/MRT;

P=/M *RT;

so P1=11.3/0.0289 *8.314* 625 = 2031.751MPa;

so 2031.751 * 4000=P2*625 => P2=13003.2064 MPa;

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