= 10.9. The compression ratio of truck diesel engines must be set at about 16 so that the engine will start when cold. Using Eqs. (10.35) to (10.37) develop a graph of 7d (in degrees) as a function of compression ratio for re 12 to 20. Assume p = 1 bar, T, = 255 K, n = 1.13, speed = 100 rev/min, bore = stroke = 120 mm, fuel cetane number = 45. If the ignition delay must be less than 20 CA for satisfactory starting, what compression ratio is required?