Introduction to Turbocharging and Turbochargers

Abstract

Supercharging can be defined as the introduction of air (or air/fuel mixture) into an engine cylinder at a density greater than ambient. This allows a proportional increase in the fuel that can be burned and hence raises the potential power output. The principal objective is to increase power output, not to improve efficiency, although the efficiency may benefit. The effect of supercharging on power output can be seen from a cylinder pressure/volume (P-V) diagram. Figure 1.1 shows an ideal naturally aspirated dual-combustion cycle. Point 1 denotes the beginning of the compression stroke when the piston is at bottom dead centre (BDC). Process 1–2 is the compression stroke. 2–3 is the part of the combustion process occurring (instantaneously) at constant volume (top dead centre, TDC). 3–4 is the remaining part of the combustion process occurring at constant pressure while the piston is moving along the cylinder. 4–5 is the continuation of the expansion process following the end of combustion. At point 5 the exhaust valve opens, allowing some exhaust gas to leave the cylinder and the pressure to fall back to the ambient level. The intake and exhaust processes are not shown.