The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Both valves are closed during compression and combustion so that the combustion chamber is sealed.
Diagram
The engine operation
Diesel engine is an internal combustion engine in which the chemical energy of fuel is transformed into thermal energy of the cylinder charge, in consequence of the self-ignition and combustion of fuel in the engine cylinder after compression of the air charge in the cylinder
There are two types of diesel engines, two-stroke and four-stroke.
In a two-stroke engine the piston is forced from the top of the cylinder by the expanding air fuel mixture. As the piston moves it is compressed, the spark plug ignites combustion, and exhaust exits through another hole in the cylinder. A two-stroke engine has no moving valves, and the spark plug fires each time the piston hits the top of its cycle, a two-stroke engine produces a lot of power for its size because there are twice as many combustion cycles occurring per rotation. However, a two-stroke engine uses more gasoline and burns lots of oil, so it is far more polluting
The 4 stroke engine refer to induction, compression, combustion and exhaust stroke that occur during two crankshaft rotation per working cycle of diesel engine.
The valves are typically operated by a , with a series of cams along its length, each designed to open a valve appropriately for the execution of intake or exhaust strokes while rotating at half crankshaft speed. A tappet between valve and cam furnishes a contact surface on which the cam slides to open the valve. The location of the camshaft varies, as does the quantity. Most engines use , or even , as in the illustration, in which cams directly actuate valves through a flat tappet. This design is typically capable of higher engine speeds because it gives the most direct and shortest inelastic path between cam and valve. In other engine designs, the cam shaft is placed in the crankcase and its motion transmitted by a push rod, rocker arms, and valve stems.
(b) A running test and energy balance of a diesel engine
Aim
The aim of this experiment is to investigate a test on a modern multi-cylinder diesel engine in order to draw up an energy balance for the engine, showing how the energy supplied to the engine can be evaluated.
Equipment
Engine: Peugeot four cylinder, four stroke, 2.3 litre diesel engine.
Output: Heenan-Froude water dynamometer
Temperatures: Thermocouples
Cooling water flow: Flowmeter
Fuel consumption: Stopwatch and 50, 100, or 200 ml pipettes.
Air flow: Air drum with 60mm orifice and inclined water manometer
Atmospheric pressure: Mercury barometer
Fuel specific gravity: Hydrometer
Procedure
The engine was warmed up and run at a steady speed of 2500 rev/min and at high throttle opening until all temperatures had stabilised. A set of readings was then taken as follows:
Atmospheric pressure p (mm. Hg)
Dynamometer:
Added mass m (kg)
Spring balance reading S (N)
Engine speed N (rev/min)
Fuel:
Lower calorific value LCV = 43 (MJ/kg)
Density (kg/ l) = 0.854 kg/l
Volume V (m/l)
Consumption time t (s)
The throttle was then partly closed, the temperatures allowed to stabilise for about 10 minutes and a further set of readings was then taken.
Results
Calculation
-
energy supplied to the engine in the fuel (Qr)
Energy supplied per second =
kw
For mass 0 kg →
-
shaft power ()
kw
Thermal Efficiency = ______shaft power____________
Energy supplied to engine fuel
= 675.29
Specific fuel consumption = Fuel mass flow rate per hour
Shaft power Kw
