3. Supercharging

Historically, diesel engine was supercharged to increase power. The charger was run by mechanically by the engine crankshaft. This enabled airflow as a function of engine speed, ideal for a piston engine. However, as it would, it wasted a lot of exhaust energy and turbocharging was invented where the turbine driven by the exhaust gases drives the compressor. This has its own problems like mismatch in air flow in terms of lower airflow than required at lower speed range and higher airflow at higher speed range. This was resolved by various techniques. The easiest, but not the most efficient, method is waste gating the turbocharger. Variable turbine entry turbocharger, two stage turbocharger and other ingenious solutions increased the overall efficiency of the engine and improved the power to weight ratio of the diesel engine. Surging, wheel speed and choking are the boundaries of operation of a turbo compressor. The boundaries are stretched by new designs of the compressor wheel. With the advent of electronics intelligent control of turbocharger enabled enhancing the airflow in the low speed range and hence the engine torque. Charge air cooling plays an important role in increasing the air flow, reducing nitric oxide emissions as well as the power. The development of turbochargers is continuing with new concepts that enhance power, engine efficiency as well as emissions.