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49 Cards in this Set
- Front
- Back
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3 main types of fuel and characteristics |
Oil - transportable - medium energy content Used for transport (high energy density) Gas - stationary use - cleanest - difficult to transport Coal -stationary power - lowest energy content - not easily transportable |
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Oil refinery process |
Fractional distillation - lowest boiling point to highest |
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Reserves |
- Proved reserves (P90): 90% confidence of being recovered (1P) - Unproved reserves: • Probable reserves (P50) 50% confidence of being recovered (2P) • Possible reserves (P10) atleast 10% chance of being recovered (3P) |
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Resources |
Reserves plus other potential sources - Contingent resources: Quantities of petroleum potentially recovered from known accumulations - Prospective resources: Quantities of petroleum potentially recovered from undiscovered accumulations |
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Petrol |
- Boiling ranges between 25 and 225°C - C8H18 |
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Diesel |
- Boiling ranges from 180 to 360°C - C12H23 |
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Difference between diesel and petrol (Molecular weight) |
-Molecular weight and boiling point greater for diesel, makes it suitable for large capacity compression ignition engines - leads to high T and P - Diesel refined at high T - Diesel is denser and less explosive |
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Fuel Volatility |
- Tendency of a liquid to evaporate - Fuel must contain large proportion of volatile components to ensure good cold start - Not too high or else vapour lock |
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Vapour lock |
When liquid fuel changes state from liquid to gas whilst still in fuel delivery system |
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Flash point |
Lowest temperature of a flammable liquid at which it can form an ignitable mixture in air |
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Fire point |
Higher temp than flash point Where vapour continues to burn after being ignited |
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Calorific value |
Index of energy in fuel Low value, more fuel needed |
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Vapour/Liquid ratio |
Ability of fuel to form bubbles |
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Knock inhibitors |
Stops engine knock by increasing octane number |
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Engine knock |
Irregular combustion/explosions in petrol engine, a-f mixture ignites too early or spontaneously |
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How to determine fuel quality |
High Octane number for petrol High Cetane number for diesel |
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octane/cetane rating |
-Measure resistance to knocking/igniting randomly -Inverse relation between them -Measures fuels tendency to burn |
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Diesel cycle |
1-2 compression2-3 fuel injection, expansion at const P3-4 Adiabatic expansion4-1 const volume heat rejection |
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Petrol (Otto) cycle |
1-2 adiabatic compression 2-3 heat addition at const volume 3-4 adiabatic expansion 4-1 heat rejection |
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Difference between diesel and petrol (Otto) cycle |
Heat added for diesel at const P but const vol for Otto |
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Ideal dual cycle |
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Indicator diagram |
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Indicated work on indicator diagram |
Space between expansion and compression minus pumping work |
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Thermal efficiency |
Indicated power output divided by fuel power input |
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Indicated work/cycle formula |
Indicated mean effective pressure (imep) x Vs (Swept volume) |
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Brake mean effective pressure |
Indicated work minus engine friction |
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Brake work/cycle formula |
Brake mean effective pressure (bmep) x Vs (swept volume) |
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Mechanical efficiency |
bmep divided by imep |
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Brake power output |
Bmep x Vs x N N is number of working strokes N= rpm/120 for 4 stroke N= rpm/60 for 2 stroke |
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Volumetric efficiency |
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Specific power output (bhp/litre) or (bhp/engine weight) |
Proportional to (N times thermal, mechanical and volumetric efficiencies) divided by weight |
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Brake thermal efficiency |
Brake work divided by Qin |
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How engine works |
- compress working fluid - injection of heat into fluid (heat input) - recover a greater amount of work (converted from heat) - removal of heat |
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2 stroke engines |
Petrol 2 stroke light weight and portable - for motor cycles Diesel 2 stroke for large applications - marine propulsion, locomotives etc |
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2 stroke IC engine |
stroke 1: fuel air mixture introduced into the cylinder then compressed stroke 2: products expands doing work and then exhausted |
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Advs and Disadvs of 2 stroke ICs |
Advs: power to weight ratio, simple design Disadvs: Emission problems and cooling and lubricating requirements |
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4 stroke spark ignition engine |
Stroke 1: a/f mixture introduced through intake valve Stroke 2: mixture compressed Stroke 3: Gas expands doing work Stroke 4: Product gases pushed through exhaust |
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Advs of 4 stroke SI engines |
-Low cost - Good power to weight ratio - High efficiency - Simple and robust - Lower emissions |
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4 stroke CI (Compression Ignition) engine |
Stroke 1: Air introduced Stroke 2: Air is compressed Stroke 3: Combustion (At const P) occurs and fuel injected Stroke 4: Expansion and gases do work and leave through exhaust |
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Difference between spark ignition and diesel engines |
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How engine works mechanically |
Indicated work |
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How to increase power |
Vd Engine size VdCompression ratio rcEngine speed N Compression ratio rcEngine speed N rc rcEngine speed N Engine speed N |
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Adiabatic gas law |
pV = mRT |
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Equations |
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Throttling Process |
Flow process experiencing a pressure drop |
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Specific fuel consumption |
bmep = (2Pi*T*nR)/Vd Wb = (2Pi*N)*T |
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Thermal efficiency |
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Combustion efficiency |
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Fuel conversion efficiency |
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