Abstract
Diesel engines are required to reduce exhaust emissions during real-world operations. In this regard, a new control concept called model-based control has been explored. Unlike the conventional method of relying on steady-state measurements, model-based control allows cycle-by-cycle optimization of control inputs based on physical principles. Existing models for combustion control have been using empirical equations to predict polytropic index for the compression stroke for estimation of in-cylinder pressure and temperature at fuel injection. Therefore, in this study, a polytropic index prediction model was developed in MATLAB to maintain the engine performance under transient conditions and to reduce the required number of experiments. The model includes a heat loss model and a gas flow model to consider the effect of wall heat transfer and gas flows inside the cylinder. The computational load of the model was reduced through discretization of a single engine cycle into several calculation points. The model was validated against numerical simulation results under steady conditions first, and then applied to transient conditions for more realistic operational conditions. The model estimated the polytropic index with average errors under steady and transient conditions with 0.22% and 0.37%, respectively. Finally, the calculation time of the model was evaluated to be 50.6 μs. It was concluded the model can be implemented on a model-based controller in the future.
Highlights
In recent years, Real Driving Emissions (RDE) has been introduced, and diesel engines are required to deliver low emissions under steady-state test bed conditions and during real-world operations
One study [4] has shown that the cylinder wall temperature takes very long time (60-100 seconds, which corresponds to hundreds of engine cycles) to reach its thermal equilibrium
A new control method called ModelBased Control (MBC) utilizes on-board models based on physical principles for real-time optimization of control inputs at each engine cycle
Summary
Real Driving Emissions (RDE) has been introduced, and diesel engines are required to deliver low emissions under steady-state test bed conditions and during real-world operations. MBC can shorten the development process for control maps and empirical equations because experiments are optional, it can maintain the engine performance under transient conditions. In the combustion model for diesel engines with multiple fuel injections developed by Yamasaki et al [14], a single engine cycle was discretized into several calculation points in an effort to reduce computational load. The authors had previously developed a theoretical heat loss model [24] based on the continuity equation and the law of conservation of energy, considering formulation of boundary layers inside the combustion chamber, while keeping the computational load low. The objective of this study is to develop an on-board polytropic index prediction model for the compression stroke of diesel engines that is reliable under transient driving conditions. The calculation speed of the model is investigated for its possibility to be implemented on a model-based controller in the future
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