A simplified representation of the Diesel cycle, with just air as the work- ing substance, is as shown in Figure 4-18. Show that the efficiency of this engine is n=1– (1/rð)-(1/rð)` Y (1/re)-(1/rc) where r₁ = V³/V2, the expansion ratio, and rc= V3/V₁, the compression ratio. If r = 5, r = 15, and y = 7/5, evaluate η. Notice that the compres- sion ratio can be much higher in a Diesel engine than in an internal combustion engine. That is because Diesel engines do not suffer from pre-ignition, as the fuel is sprayed in at the end of the compression stroke; this allows an increased rc. This is one reason why Diesel engines are more efficient than internal combustion engines. 4-18 P b C Adiabat d Adiabat V2 20 V3 V

A simplified representation of the Diesel cycle, with just air as the work- ing substance, is as shown in Figure 4-18. Show that the efficiency of this engine is n=1– (1/rð)-(1/rð)` Y (1/re)-(1/rc) where r₁ = V³/V2, the expansion ratio, and rc= V3/V₁, the compression ratio. If r = 5, r = 15, and y = 7/5, evaluate η. Notice that the compres- sion ratio can be much higher in a Diesel engine than in an internal combustion engine. That is because Diesel engines do not suffer from pre-ignition, as the fuel is sprayed in at the end of the compression stroke; this allows an increased rc. This is one reason why Diesel engines are more efficient than internal combustion engines. 4-18 P b C Adiabat d Adiabat V2 20 V3 V