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In order to counteract the drawbacks of conventional diesel combustion, which can lead to high indicated specific nitric oxide and indicated specific particulate matter emissions, a promising diesel-dual-fuel concept is investigated and evaluated. In this study, methane is used as supplement to liquid diesel fuel due to its benefits like high knock resistance and clean combustion. A deep understanding of the in-cylinder process is required for engine design and combustion controller development. To investigate the impact of different input parameters such as injection duration, injection timing, and substitution rate on varying output parameters like load, combustion phasing, and engine-out emissions, numerous investigations were conducted. Engine speed, global equivalence ratio, and injection pressure were held constant. The experiments were carried out in a modified single-cylinder compression ignition engine. The results reveal regimes with different dependencies between injection timing of diesel fuel and combustion phasing. This work demonstrates the potential of the diesel-dual-fuel concept by combining sophisticated combustion control with the favorable combustion mode. Without employing exhaust gas recirculation, TIER IMO 3 emissions limits are met while ensuring high thermal efficiency.

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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.

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