Diesel Engine Classification

Diesel Engine

►In 1892 Dr. Rudolf Diesel obtained his first patent.

►The engine ran on coal dust with a 1,500 psi compression pressure and no cooling.

►The idea was to have such an efficient engine that the expansion would take care of the cooling

►The engine blew up and almost killed Dr. Diesel.Source: Marine Diesel Engines by Daniel Charnews

Diesel Engine

►In 1895 Dr. Diesel tried again with an engine that had a compression pressure of 450 psi.

►The engine was water cooled, had air blast injection and ran on fuel oil.

►The engine ran at 24 percent efficiency.

►Dr. Diesel’s goal was to build a engine which approached the theoretical efficiency of his first engine.Source: Marine Diesel Engines by Daniel Charnews

Diesel Engine

►Chemical Energy (Fuel Supplied to the Engine).

►Thermal Energy (Combustion raises air/fuel temperature and pressure).

►Mechanical Energy (Piston moves because of high pressure exerted upon it).

►Work (Shaft rotates after translating piston motion).

Diesel Engine

►Overall Efficiency (ηOverall) = Shaft work developed/Chemical energy supplied

►Mechanical Efficiency (ηMech) = Shaft work developed/Indicated work by the combustion gas

►Cylinder bore = Cylinder diameter.►Piston Stroke = Distance from Top

Dead Center (TDC) to Bottom Dead Center (BDC)

Diesel Engine

►Piston Displacement = Cylinder area X Stroke = (Π/4)d2L

►Net Work (Wnet) = Mean Effective Pressure (mep) X Piston Displacement.

►Power = number of power revolution (n) X Wnet = (mep)LAn

Engine Classification

►Slow speed: 0 – 200 RPM*►Medium speed: 200 – 1200 RPM*►High speed: 1200 – 2500 RPM*►Ultra high speed: 2500 RPM – above*►* RPM at the crankshaft

Engine Classification

►Piston Speed ft/min = (2 X Stroke X RPM)/12)

►Speed factor = (Piston Speed X RPM)/100,000

Engine Classification

►3 or below: Slow Speed►3 to 9: Medium Speed►9 to 27: High Speed►27 and up: Ultra High Speed

Four Stroke Cycle

►Four Stroke Cycle requires the engine to complete two revolutions or 720 ° to complete the cycle.

►There is only one power stroke every two revolutions.

►The cycle requires four different strokes to complete the cycle

►Cylinder is equipped with both intake and exhaust valves.

Four Stroke Cycle

►Intake Stroke: The intake valve is open, the exhaust valve is closed, and the piston moves down, bringing in fresh air into the cylinder.

►Compression Stroke: Both intake and exhaust valves are closed, and the air is compressed by the upward movement of the piston.

Four Stroke Cycle

►Power Stroke: Both the intake and exhaust valves are closed and combustion occurs with a resultant increase in pressure, forcing the piston downward.

►Exhaust Stroke: The exhaust valve is open, the intake valve is closed, and the upward movement of the piston forces the products of combustion from the engine.

Two Stroke Cycle

►The two stroke cycle has a cylinder arrangement of intake and exhaust ports or intake ports and exhaust valves.

►The two stroke cycle engine has a power stroke every revolution.

►The intake, compression, power and exhaust processes must occur within each revolution.

Two Stroke Cycle

►To assist the exhaust process the engine is equipped with scavenging blowers which raise the inlet air pressure above atmosphere.

►The intake air pushes the exhaust air out.

►The combustion process does not go as far as it does in the four stroke cycle, so the work is not twice that of the four stroke.

Diesel Engines

►Brake Horsepower (BHP) – Is the actual power output at the end of the crankshaft available for doing work.

►BHP = ((2Π X F X R X N)/33,000)►F = The force exerted at a known

radius (R)►R = Radius of the flywheel in ft.►N = Number of revolutions of the

crankshaft

Diesel Engines►Indicated Horsepower (IHP) – Is the

power developed in the cylinder.►IHP = ((P X L X A X n)/33,000)►P = Indicated mean effective pressure,

psi►L = Piston stroke, ft►A = Piston area, in2

►n = Number of power strokes►For a 2 cycle engine n = RPM►For a 4 cycle engine n = RPM/2

Diesel Engines

►Friction Horsepower (FHP) – Are the losses which the engine has due to friction between moving parts, the work which is required to pull in the air and push out exhaust gases (pumping losses).

►Basically FHP is the measure of the power used up in running the engine.

►BHP = IHP - FHP

Diesel Engines

►Mechanical Efficiency (ηMech) = BHP/IHP

►Overall Efficiency (ηOverall) = BHP/ Heating Value of the Fuel

Diesel Engines

►Brake Specific Fuel Consumption (bsfc) – The fuel economy of the engine expressed as pounds of fuel consumed per brake horsepower for a period of one hour (lb per bhp per hr).

►bsfc = (lbs of fuel burned per hr/bhp) or

►bsfc = (lb per bhp hr X heating value)

Diesel Engines

►bsfc = ((ft3 of gas burned X heating value X 60)/(length of test (min) X BHP)) (for natural gas)

►Indicated Thermal Efficiency (ηit) - Ratio of work done in a unit of time to the total heat supplied in the same unit of time.

►ηit = ((Heat equivalent of one HP hr (BTU) X IHP)/(lb fuel used per hr X Heating Value of fuel)) (BTU per lb)

Diesel Engines

►Brake Thermal Efficiency (ηib) - Ratio of work done in a unit of time to the total heat supplied in the same unit of time.

►ηib = ((Heat equivalent of one HP hr (BTU) X BHP)/(lb fuel used per hr X Heating Value of fuel)) (BTU per lb)

►ηib = ((Heat equivalent of one HP hr (BTU))/ (brake specific fuel consumption))

Diesel Engines

►If a 4 – cycle engine has six cylinders with a 8 inch bore, a 10 inch stroke and develops an imep of 120 psi operating at 800 rpm. What will be the indicated horsepower (IHP) ?

►IHP = ((P X L X A X n)/33,000)

►IHP = ((120 X (10/12) X (Π/4 X 82) X (6 X 800/2)) / 33,000)

Diesel Engines

►IHP = ((120 X 10 X 3.1416 X 64 X 6 X 800) / (33,000 X 12 X 4 X 2))

►IHP = 365 H.P.

Diesel Engines

►If an engine develops 1000 bhp and burns 75 lb of fuel oil in 10 minutes. What is the brake thermal efficiency if the heating value is 19,000 BTU per lb?

►ηib = ((Heat equivalent of one HP hr (BTU) X BHP)/(lb fuel used per hr X Heating Value of fuel)) (BTU per lb)

►The heat equivalent of one horsepower delivered for a period of one hour is 2545 BTU

Diesel Engines

►ηib = ((2545 X 1000) / (75 X 6 X 19,000))

►ηib = 0.298 = 29.8%