Triple-injection strategy for model-based control of premixed charge compression ignition diesel engine combustion

Abstract

Low-temperature combustion concepts are of great interest due to their potential to reduce nitrogen oxides (NO_x) and soot simultaneously. However, low-temperature combustion often leads to an increase in total unburnt hydrocarbons and carbon monoxide. Furthermore, combustion sound level becomes a challenge, especially at higher loads. Various studies show that these drawbacks can be compensated by advanced injection strategies, for example, split injections. In this study, a significantly modified triple-injection approach is proposed. First, the corresponding impact on engine performance is evaluated at stationary conditions, and second, its observed advantages are evaluated at transient operation. Stationary results show that NO_x, soot, and combustion sound level are simultaneously reduced without losses in fuel efficiency and without any remarkable rise in total unburnt hydrocarbon as well as carbon monoxide emissions, satisfying Euro 6 emission regulations. Under transient conditions, model-based predictive control of the engine, which allows for reliable steady-state measurements and permits validation tests at transient operating points, is successfully demonstrated for single and triple injection. With both injection strategies, control of indicated mean effective pressure, combustion phasing (CA50 (crank angle (CA) when 50% fuel is consumed)), and NO_x emissions is achieved. As a result of this work, the identified optimal triple-injection strategy leads to lower total unburnt hydrocarbon emissions and to significantly reduced combustion sound level at the same level for NO_x emissions in comparison with the single-injection approach. Thus, the proposed triple-injection strategy combined with sophisticated model-based control is a promising concept for future engine emission control.