Turbo compressor drives greener engines

Problem: But a conventional compressor only operates effectively over a limited range of air flow rates. When the air flow drops below a critical level, a condition known as surge occurs. This results in the air flow becoming unstable and the compressor stalls. Solutions to this problem have been applied in motorsport and high performance road car applications, often making use of adjustable vanes to match compressor geometry to flow rate. Such devices are mechanically complex, expensive and can generate high pressure losses, so their uptake in volume production applications has remained low. Solution: Engine technology specialist Integral Powertrain (IP) has developed a method that enables compressors to operate efficiently across a wider range of mass flow rates, giving improved fuel economy and power output. The innovation is a simplified 'pre-whirl generator' system which uses guide vanes in the gas inlet path to introduce axial rotation to the flow. This rotation changes the angle at which the incoming air strikes the compressor blades. The company told Eureka that "by adding a precise amount of rotation, the system extends the range of efficient operating flow rates by as much as 20%." To ensure the right degree of 'pre-whirl' the system uses two coaxial air paths - an outer path with guide vanes and an inner one without. Each path is regulated by a simple valve mechanism on a common shaft, which can be controlled by a single actuator. This splits the incoming air proportionally between the two paths. When the flow recombines, a pre-determined amount of whirl is produced. Applications: The characteristics of the system make it ideal for the next generation of high output diesel engines. Using CFD, IP has demonstrated that the system is capable of extending the compressor operating range by 20%, giving improved low speed torque and enhanced driveability. IP's technical director Luke Barker commented: "We've managed to achieve a robust, easily controlled solution that can be manufactured from inexpensive materials and our analysis indicates that the system will operate with minimal pressure loss in the intake system, so maximum operating efficiency is maintained." DP