Automotive Engines: IC Engine Principles, Fuel, Cooling, Lubrication and Emission Control
The engine domain tests the thermodynamics, fuels and auxiliary systems that keep an internal combustion engine running and legal.
Cycles and fuel
- The four-stroke SI engine draws a petrol-air mixture, compresses it, ignites it with a spark and exhausts; the CI engine compresses air alone and injects diesel that self-ignites. Typical compression ratios: petrol 8:1–12:1, diesel 16:1–22:1.
- Petrol quality is rated by octane number (resistance to knock, roughly 91 RON in India); diesel by cetane number (ignition ease, minimum 51 under BS-VI). Knocking is worsened by low octane, over-advanced timing, excessive compression ratio and hot spots.
Cooling and lubrication
- Cooling may be thermosyphon or pump-circulated; the thermostat opens around 82–90 °C and a pressurised radiator cap raises the boiling point. Lubrication may be splash or pressure-fed from a wet sump; oil seals, cleans, cools and reduces friction, and SAE 10W-30 is a multi-grade example.
Emission control
- BS-VI came into force on 1 April 2020, with fuel sulphur cut from 50 ppm to 10 ppm. Petrol engines use a three-way catalytic converter with lambda control for CO, HC and NOx; diesel engines combine a diesel oxidation catalyst, a diesel particulate filter and selective catalytic reduction with AdBlue. EGR lowers NOx by diluting the charge.
Worked example
Bore 80 mm, stroke 90 mm: swept volume = (π/4) × 8² × 9 = 452.4 cm³. With clearance volume 45 cm³, compression ratio = (452.4 + 45) ÷ 45 = 11.05:1 - a realistic petrol value.
Traps
- Swapping octane and cetane, or dividing by swept volume instead of clearance volume.
- Assigning the DPF and SCR the same job; SCR treats NOx, the DPF traps soot.