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))