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ElsevierMolina Alcaide, SA.; García Martínez, A.; Pastor Enguídanos, JM.; Belarte Mañes, E.; Balloul, I. (2015). Operating range extension of RCCI combustion concept from low to full load in a heavy-duty engine. Applied Energy. 143:211-227. doi:10.1016/j.apenergy.2015.01.035. overlimit function is used to select the best engine settings for each operating point. 23Finally, engine emissions and performance results from that RCCI operation are 24 compared with conventional Diesel combustion (CDC). 25Results suggest that double injection strategies should be used for RCCI operation from 26 low to mid load. However, from high to full load operation, single injection strategies 27 should be used, mainly to avoid excessive in-cylinder pressure gradients. In addition, it 28 is confirmed the suitability of RCCI combustion to overcome the soot-NOx trade-off 29 characteristic of CDC, from 6 to 24 bar of BMEP, while improving fuel consumption. 30

a b s t r a c tThis work investigates the capabilities of the dual-mode reactivity controlled compression ignition/conventional diesel combustion engine operation to cover the full operating range of a EURO VI medium-duty diesel engine with compression ratio of 17.5:1. This concept is based on covering all the engine map switching between the reactivity controlled compression ignition and the conventional diesel combustion operating modes. Specifically, the benefits of reactivity controlled compression ignition combustion are exploited whenever possible according to certain restrictions, while the conventional diesel combustion operation is used to cover the zones of the engine map in which the reactivity controlled compression ignition operation is limited.The experiments were conducted using a single-cylinder research diesel engine derived from the multi-cylinder production engine. In addition, considering the mandatory presence of biofuels in the future context of road transport and the ability of ethanol to be blended with gasoline, the low reactivity fuel used in the study is a blend of 20% ethanol by volume with 80% of 95 octane number gasoline. Moreover, a diesel containing 7% of biodiesel has been used as high reactivity fuel. Firstly, a reactivity controlled compression ignition mapping is performed to check the operational limits of the concept in this engine platform. Later, based on the results, the potential of the dual-mode concept is discussed.Results suggest that, under the constraints imposed, reactivity controlled compression ignition combustion can be utilized between 25% and 35% load. In this region of the map, reactivity controlled compression ignition can provide up to 2% increased gross indicated efficiency than conventional diesel combustion, but led to lower efficiency at low engine speeds. In addition, it was demonstrated that the regeneration periods of the diesel particulate filter during dual-mode operation can be reduced more than twice, which entails a great reduction of the diesel fuel amount injected in the exhaust line.

This work investigates the load limits of reactivity controlled compression ignition (RCCI) combustion, a dual-fuel concept which combines port fuel injection of low reactivity fuels with direct injection of diesel fuel, in a medium-duty diesel engine. The experiments were conducted in a single-cylinder diesel engine derived from the multi-cylinder production engine. In this sense, the stock turbocharger and exhaust gas recirculation (EGR) systems were replaced by an external compressor and dedicated low pressure EGR loop, respectively. Additionally, a port fuel injector was installed in the intake manifold to allow gasoline injection. Firstly, the paper presents some results highlighting the effect of the EGR rate, gasoline fraction (GF), diesel start of injection (SOI), diesel injection strategy and intake temperature on the emissions, performance and combustion development in a representative operating condition; 1200 rpm and 6.5 bar IMEP (25% load). Later, with the aim of showing the RCCI potential, the best results in terms of performance and emissions at 25% load are compared against the multi-cylinder diesel engine from 950 to 2200 rpm. RCCI engine tests were developed taking into account limitations in nitrogen oxides (NOx) and soot emissions, in-cylinder pressure and maximum pressure rise rate. Finally, keeping the same constraints for testing, the load limits of RCCI concept are evaluated for all the engine speeds. Results suggest that RCCI allows fulfilling EURO VI limits for NOx and soot emissions without using selective catalytic reduction (SCR) and diesel particulate filter (DPF) aftertreatment systems at 25% load at all engines speeds, providing better indicated efficiency than conventional diesel operation in most operating points. In addition, the maximum engine load that ensured the aforementioned constraints was around 35% for all engine speeds, with a maximum IMEP of 8.8 bar at 2200 rpm. In this case, a strong reduction in carbon monoxide (CO) and unburned hydrocarbons (HC) emissions compared to the cases of 25% load was achieved at all engine speeds.