Independent fuel injection strategy based on the initial piston positions for HEV engine quick start

Engine start/stop strategy is one of the most important methods for hybrid electric vehicles (HEVs) to achieve fuel economy and low emission. The engine of HEV would experience frequent start/stop during a normal drive. In this paper, an independent fuel injection strategy (IFIS) for port fuel injection (PFI) engine was proposed to realize a quick HEV hot start with low-emission. The purpose of the IFIS is to supply fuel injection independently for each cylinder according to their initial piston positions (IPPs) at the beginning of the cranking start. With independent injection timing and optimized fuel pulse width (FPW), appropriate mixtures can be produced for all cylinders shortly after the start of cranking. Thus, robust and stable combustion could be obtained. By introduction of the IFIS, not only HEVs could experience better startability and lower hydrocarbon (HC) emissions during hot re-starts, but also vehicles with conventional drivetrain would have start-stop capabilities. In this work, the mixture preparation characteristics based on four typical IPPs were studied at first. Then the IFIS was proposed and experimentally tested. The results of the IFIS tests are compared with the original fuel injection strategy (OFIS) of the engine control unit (ECU) in terms of the starting time, indicated mean effective pressure (IMEP) and engine-out hydrocarbon (EOHC). The results of the IFIS tests suggest that the IFIS is a very effective method to improve the HEV hot start. With IFIS, shorter starting time and lower HC emissions were both achieved.