Active charge air cooling

Boosted IC engine development, both diesel and gasoline, is driving the need for better charge air temperature control. Charge air temperature directly and indirectly influences engine performance, fuel economy & emissions. To date charge air temperature control has, in the main, been passive; aiming only to reduce temperatures towards, but still above, ambient temperature. Driven by increasing specific output, the opportunities for sub-ambient charge cooling need to be investigated. For some real world driving conditions it is also desirable to raise the charge temperature. Air Cycle Technology ltd (ACT), working with the University of Huddersfield (UoH) are developing a controllable charge air cooling system, which will deliver charge air at sub-ambient temperature over a wide engine operating range. The system uses a turbo-expander to deliver air-cycle cooling in a simple and practical way. The system can be enhanced by combination with a charge air heating process. Accurate charge temperature control over as wide an engine operating range as possible is also addressed. The system is fully compatible with the operational, packaging and cost needs of vehicle OEMs. The paper presents the principle, process and application of a controllable charge air cooling/heating system. It covers the design and operation of the turbo-expander which delivers sub-ambient charge temperatures, the option of charge air heating and possible control methods. Examples of specific engine applications are presented to clearly indicate the opportunities for improvements in engine performance and fuel economy