Example Problem 2.2 The self-ignition temperature (SIT) of a fuel is, as discussed in Chapter 6, the temperature at which the fuel will self-ignite. A diesel engine will not start unless the temperature at the end of the compression stroke is greater than the SIT of the fuel. Given that the SIT of diesel fuel is 387C (729F) and that the air temperature in the combustion chamber is 20C (68F) at the beginning of the compression stroke, will Basic Thermodynamics of Engines 23 the air be hot enough to ignite the fuel if it is compressed to one-sixteenth of its initial volume? (Assume n = 1.3) Solution: The absolute temperature T = 20C + 273 = 293K (T = 68F + 460 = 528R). The temperature T2 at the end of the compression stroke (Figure 2.1) is: T = 293[16/1]1.3-1 = 673K or = T2 673K 273 = 400C (T2 = 528[16/1] 1.3-1 = 1213R) (T = 1213R - 460 = 753F) The temperature T2 is above the SIT of the fuel, and therefore, the fuel will self- ignite from the compression.