Benchmarking optimised camshaft profiles for an FSAE turbocharged engine

Abstract

Formula SAE is a student-based educational motorsport competition held across the globe in which university students are challenged to conceive, design, fabricate and compete with single seater open wheel race cars. Regulations set by the SAE create limitations that promote students to create innovative solutions and develop their problem-solving skills. Internal combustion regulations stated that the engine used to power the vehicle must not exceed 610cc per cycle and power is limited by a single 20mm diameter restrictor in the air intake [1]. Thus, it was decided that a Kawasaki ZX6R engine would be turbocharged to maximise air flow through the restrictor. Since the engine was not designed for turbocharged applications, it featured a high valve overlap which at low engine speeds forces part of the mixture of air and fuel from the intake stroke to escape from the closing exhaust valves. To counteract the air-fuel mixture loss, in a previous project a set of optimised camshafts were designed, however they were never tested on the engine. The main aim of this project was to benchmark the set of optimised camshafts with the OEM variants and analyse the results. To carry out the benchmarking process the engine test stand had to be modified with additional sensors and hardware changes to allow extensive engine mapping. Four engine test speeds at two different Manifold Absolute Pressure levels were selected as steady state test zones to analyse the camshaft performance. The optimised camshafts proved to allow the engine to flow around 10% more air at 125 kPa across the test engine speed range. At 150 kPa similar performance figures were experienced except for the 10000 RPM case. Since at this test point no increase in power and MAF was experienced with the optimised camshafts, it was concluded that the choke limit of the restrictor was reached. An average increase of 6% in volumetric efficiency was gained across the tested setpoints with the exclusion of 5000 RPM 150 kPa. Furthermore, an overall decrease in BSFC of a 9% average was experienced except for two setpoints which operated at slightly rich AFRs. Ricardo Wave simulations were carried out to confirm the performance gains of the optimised camshafts obtained from experimental testing. Furthermore, Wave was used for exhaust valve anchor timing where the effects of the anchor timing on MAF were analysed and the optimum shift angle of 7.5° later in the four-stroke cycle was found.