Design for Manufacture

4. Petrol Engines

Design for Manufacture

Design for Manufacture

Design for Manufacture

Design for Manufacture

Briggs & Stratton Engine

Design for Manufacture

Petrol Engines for Lawnmowers Quantum

Design for Manufacture

Design for Manufacture

Design for Manufacture

Design for Manufacture

Otto cycley

An 'Otto cycle' is an idealized thermodynamic cycle, describing the f i i f i l k i i i i i i ifunctioning of a typical spark ignition reciprocating piston engine

1-2 isentropic compression2-3 constant-volume heat transfer3 4 isentropic e pansion (po er stroke)3-4 isentropic expansion (power stroke)4-1 a constant-volume process (heat rejected)

Design for Manufacture

Design for Manufacture

Design for Manufacture

Idealised indicator diagram for 4-stroke engine

Design for Manufacture

Design for Manufacture

Stylised indicator diagram for 4-stroke engine

Engine Thermal Efficiency

Design for Manufacture

Energy Balance for per 1 kW power output

Heat Measurement Temperature t (Celsius) = T-273.15 (Kelvin) Q – heat energy joules/kgQ gy j g Specific heat capacity: heat transfer per unit temperature. Unit: joules/kg K (Joules per kg per degree)Unit: joules/kg K (Joules per kg per degree) Water: 4180 J/kg ·K Ice (-10ºC): 211 J/kg ·K S (100ºC) 208 J/k KSteam (100ºC): 208 J/kg ·K Air(room condition): 1012 J/kg ·K Copper: 385 J/kg ·K Calorific value of fuel The heat liberated by burning unit mass or volume of a fuel.

t l 43MJ/ke.g. petrol: 43MJ/kg Heat Unit Calorie 1 calorie = 4.18 joules (The heat to raise 1 degree for 1 gram water)j ( g g )

Fuel Consumption

Single cylinder 4 stroke petrol engine thermal efficiency 20-25%. Example: A 3 KW petrol engine has a thermal efficiency 20.5%. Find fuel consumption per hour. 3KW·hr= 3000J/s ×3600s=10,800,000J=10.8MJ Petrol heat energy is 43MJ/kggy g The fuel consumption:

kg23.1205.0438.10

=×

Take petrol density 719.7 kg/m3. 1.23 kg = 1.23 /0.7197 = 1.7 L