DOE-HDBK-1018/1-93FUNDAMENTALS OF THE DIESEL CYCLEDiesel Engine FundamentalsSummaryThe important information in this chapter is summarized below.Fundamentals of the Diesel Cycle SummaryIgnition occurs in a diesel by injecting fuel into the air charge which has beenheated by compression to a temperature greater than the ignition point of thefuel.A diesel engine converts the energy stored in the fuel's chemical bonds intomechanical energy by burning the fuel. The chemical reaction of burning thefuel liberates heat, which causes the gasses to expand, forcing the piston torotate the crankshaft.A four-stroke engine requires two rotations of the crankshaft to complete onecycle. The event occur as follows:Intake - the piston passes TDC, the intake valve(s) open and the fresh air isadmitted into the cylinder, the exhaust valve is still open for a few degreesto allow scavenging to occur. Compression - after the piston passes BDC the intake valve closes and thepiston travels up to TDC (completion of the first crankshaft rotation).Fuel injection - As the piston nears TDC on the compression stroke, thefuel is injected by the injectors and the fuel starts to burn, further heatingthe gasses in the cylinder.Power - the piston passes TDC and the expanding gasses force the pistondown, rotating the crankshaft. Exhaust - as the piston passes BDC the exhaust valves open and theexhaust gasses start to flow out of the cylinder. This continues as the pistontravels up to TDC, pumping the spent gasses out of the cylinder. At TDCthe second crankshaft rotation is complete. ME-01Rev. 0Page 28
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