A Simulation Study Assessing the Viability of Shifting the Location of Peak In-Cylinder Pressure in Motored Experiments

Hybrid powertrains utilize an engine to benefit from the power density of the liquid fuel to extend the range of the vehicle. On the other hand, the electric machine is used for; transient operation, for very low loads and where legislation prohibits any gaseous and particulate emissions. Consequently, the operating points of an engine nowadays shifted from its conventional, broad range of speed and load to a narrower operating range of high thermal efficiency. This requires a departure from conventional engine architecture, meaning that analytical models used to predict the behavior of the engines early in the design cycle are no longer always applicable. Friction models are an example of sub-models which struggle with previously unexplored engine architectures. The “pressurized motored” method has proven to be a simple experimental setup which allows a robust FMEP determination against which engine friction simulation can be fine-tuned. This is due to the elimination of the experimental variability introduced by combustion, whilst retaining the fired-like load on the cranktrain, as reported in SAE 2018-01-0121. It employs a “shunt pipe” recirculating air from the exhaust back into the intake, therefore requiring very little air supply demands. The temperature of the bulk gas was also maintained similar to that of a fired engine with the use of Argon as the working gas, reported in SAE 2019-01-0930. Mixtures of Argon-to-air were also used to investigate the effect of temperature on FMEP, published in SAE 2019-24-0141 and SAE 2020-01-1063. This leaves one pending criticism of the pressurized motoring method - that of having a relatively fixed location of peak pressure (≈1DegCA BTDC), when compared to a fired engine, which is around 10DegCA for CI and 20DegCA for SI. In this publication, a simulation investigation is performed to assess the viability and extent of an experimental modification to the pressurized motoring method, involving the use of small fuel injections to shift the location of peak pressure in the aim of replicating better the fired engine, whilst retaining the benefits of a motored setup.