2 What is a compression engine? Needs no spark to ignite fuel/air mixture as in a gasoline spark ignition (SI) engineCombustion occurs spontaneously due to compressionAll diesel engines are compression ignition (CI) engines
4 SI Engine with OHC Air cleaner Carburetor Camshaft Rocker arm Intake valveRocker armPistonConnecting rodCrankshaftOil pumpExhaust valveCarburetorCrank sprocketOil pickupTiming beltCam sprocketAir cleanertensor
5 Definitions Temperature /oC, F, K Volume /cm3 or cc Pressure / atm, psi, PaSee also glossary of terms
6 What is diesel? Crude oil fraction after gasoline (petrol) C9H20 – C12H26 nonane – dodecaneExact composition governed by various standards
7 The Chemistry Diesel is burnt: CnH2n+2 + O2 H2O + CO2 +HEAT Inefficient combustionCO, carbon monoxideC, soot, diesel particulatesPCAs, benzene etc.
8 4-stroke operating cycle Crank shaft90o180oBCTC0o270oqSpark plug for SI engineFuel injector for CI engineTop Center(TC)BottomCenter(BC)ValvesClearancevolumeCylinder wallPistonStroke
9 Induction Stroke Engine pulls piston out of cylinder Low pressure inside cylinder (< 1 atm.)Atmospheric pressure pushes air into cylinderEngine does work on the gases during this stroke
10 2. Compression stroke Engine pushes piston into cylinder Air is compressed to high pressure and temperature (700psi, 540oC)Fuel injected as piston reaches top of strokeEngine does work on the gases during this stroke
11 3. Power StrokeFuel/air mixture burns to form hot gases (2000oC, 1000psi)Gases push piston out of cylinderGases expand to lower pressure and temperatureGases do work on engine during this stroke
12 4. Exhaust stroke Engine pushes piston into cylinder High pressure inside cylinderPressure pushes burned gases out of cylinderEngine does work on the gases during this stroke
16 Number of cylinders Single-cylinder …engine gives one power stroke per crank revolution (2 stroke) or two revolutions (4 stroke). The torque pulses are widely spaced, and engine vibration and smoothness are significant problems.Used in small engine applications where engine size is more importantMulti-cylinder…engines spread out the displacement volume amongstmultiple smaller cylinders. Increased frequency of power strokesproduces smoother torque characteristics. Engine balance (inertia forcesassociated with accelerating and decelerating piston) better than singlecylinder.
17 Types of injection Direct injection: quiescent chamber Glow plugOrifice-plateDirect injection:quiescent chamberDirect injection:swirl in chamberIndirect injection: turbulentand swirl pre-chamber
18 Critical factors Compression must be high enough BatteriesWorn piston/barrelValve seatingFuel and air must mix thoroughlyInjectors working correctlyGlow plugs must work properly where fitted