Nowadays, improving drivability, reliability and mostly fuel economy for automotive applications became a high priority all over the world and legal requirements are focused on fuel consumption reduction and emissions, so several strategies are explored by engine researchers to satisfy these requirements, engine downsizing is potentially one of the most effective strategies.
Downsizing, reduction in engine displacement volume while keeping the same performance in terms of power and torque than the initial larger engine, can be achieved by running with high levels of pressure boosting at full load using supercharger or turbocharger.
Turbocharging combined with engine downsizing to retain power has been shown to be an effective means of improving vehicle performance, fuel consumption and emissions
1.1 Internal combustion engines
The internal combustion (IC) engine is a heat engine that converts chemical energy in a fuel into mechanical energy, usually made available on a rotating output shaft. Chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine. This thermal energy raises the temperature and pressure of the gases within the engine, and the high-pressure gas then expands against the mechanical mechanisms of the engine. This expansion is converted by the mechanical linkages of the engine to rotating crankshaft.
Internal combustion engines can be classified in a number of different ways:
1- Type of ignition:
§ Spark Ignition (SI)
§ Compression Ignition (CI)
2- Engine Cycle:
§ Four-Stroke Cycle
§ Two-Stroke Cycle
3- Air intake system:
§ Naturally Aspirated
1.2 Performance characteristics
Performance of the internal combustion engine is characterized with several geometric and thermodynamic parameters.
- Swept Volume (Vd): Volume displaced by the cylinder traveling between the BDC and the TDC. Swept Volume for an engine also known as the engine displacement; its usually expressed in cm3 (cc) or liters. Most passenger cars have a displacement within the range of 1.0-3.0 liters.
Figure()Engine cylinder schematic
- Clearance Volume: Minimum cylinder volume when the piston is at theTDC
VC = VTDC
VBDC = VC + Vd
- Compression ratio (rc): The ratio between the cylinder volume at the BDC and at the TDC, the higher compression ratio, the higher thermal efficiency.
- This is in the range of: