In a direct-injection stratified-charge (DISC) engine fuel is injected into the engine cylinder just before top-center (like a diesel); a spark discharge is then used to initiate the combustion...

In a direct-injection stratified-charge (DISC) engine fuel is injected into the engine cylinder just before top-center (like a diesel); a spark discharge is then used to initiate the combustion process. A four-stroke cycle version of this engine has a displa& volume of 2.5 liters and a compression ratio of 12. At high load, the inlet pressure is boosted by a compressor to above atmospheric pressure. The compressor is geared directly to the engine drive shaft. The exhaust pressure is 1 atm. This DISC engine is to replace an equal displacement conventional naturally aspirated spark-ignition (SO engine, which has a compression ratio of 8

(a) Draw qualitative sketches of the appropriate constant-volume ideal cycle pressure-volume diagrams for the complete operating cycles for these two engines at maximum load.

(b) Use available fuel-air results to estimate how much the DISC engine inlet pres sure must be boosted above atmospheric pressure by the compressor to provid the same maximum gross indicated power as the naturally aspirated SI engin The SI engine operates with an equivalence ratio of 1.2; the DISC engine limited by smoke emissions to amaximum equivalence ratio of 0.7.

(c) Under these conditions, will the brake powers of these engines be the same, giv that the mechanical rubbing friction is the same? Briefly explain.

(d) At part load, the ST engine operates at an equivalence ratio of 1.0 and in1 pressure of 0.5 atm. At part load the DISC engine has negligible boost an operates with an inlet pressure of 1.0 atm. Use fuel-air cycle results to determin the equivalence ratio at which the DISC engine must be operated to provide t same net indicated mean effective pressure as the SI engine. What is the ratio DISC engine net indicated fuel conversion efficiency to SI engine efficiency these conditions?