A reputable engine company has been making carburetedspark-ignition engines that operate with an equivalence ratio = 1.0and a compression ratio of 9:1 for years. In order to controlemissions, the engines operate with 20% exhaust gas recirculation(EGR) and a three-way catalytic converter. Since the company’smarket share is steadily dropping, they consider hiring a MECgraduate to rescue them. The ambitious young engineer proposes aport fuel-injected (PFI) design, which operates lean at 0.7 with ahigh compression ratio (15:1) and vigorous inlet swirl. The newengine has the spark-plug mounted at the center of the combustionchamber, while the production engine has the spark-plug at theside.

(a) Will the flame development period of the new chamber beshorter, longer, or about the same as the current design?

(b) Will the rate of the combustion of the new chamber befaster, slower, or about the same as the current design?

(c) Sketch the mass fraction burned vs. crank-angle curves forthese two combustion chambers when spark-timing is set for maximumbrake torque. Clearly label the sparktiming, ignition delay, andoverall burn duration for each case.

(d) The engineer claims that the proposed lean-burn engine willhave the same octane requirement as the production SI engine. Couldthis claim be true?

(e) Will the proposed lean-burn engine clearly develop greaterpower at full load than the current SI engine?

(f) Would there be any additional advantages or disadvantages ifthe proposed engine were direct-injected, stratified charge,instead of homogeneous, operating at the same overall equivalenceratio?