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Elevada eficiencia térmica y mínimas emisiones contaminantes impuestas por las restrictivas normativas anticontaminación en motores alternativos representan el principal objetivos de los fabricantes de motores. La estrategia de combustión diésel convencional es ampliamente utilizada en el mundo gracias a su excelente economía en el consumo de carburante. Esta estrategia permite operar con mezclas pobres de combustible y aire proporcionando elevada eficiencia térmica. Además, este tipo de combustión puede ser aplicada desde motores tanto para vehículos ligeros como en motores marinos. Sin embargo, este proceso de combustión conlleva a la generación de elevadas emisiones de NOx y emisiones de partículas (comúnmente llamado hollín en los diésel), siendo imposible reducir ambos contaminantes de forma simultánea. Por tanto, los fabricantes han incorporado sistemas de post-tratamiento con el objetivo de cumplir con las normativas de emisiones, cuya intención es la de proveer emisiones más limpias y elevada eficiencia. Por el contrario, este tipo de sistemas para mitigar las emisiones contaminantes incrementan la complejidad del motor dado el complejo proceso llevado a cabo durante el post-tratamiento y una aumento en los costes tanto de producción como operativos a lo largo del ciclo de vida del motor. La comunidad científica continua desarrollando soluciones alternativas a la combustión diésel convencional manteniendo los beneficios de este proceso de combustión mientras que las emisiones son reducidas (principalmente NOx y hollín). La comunidad científica ha encontrado en las estrategias de combustión de baja temperatura un proceso de combustión capaz de proporcionar elevada eficiencia térmica y emisiones ultra bajas de NOx y humo. En este sentido, la revisión bibliográfica dice que estos tipos de combustión permiten la reducción simultánea de ambas emisiones, rompiendo así el tradicional "trade-off" existente en la combustión diésel convencional. Sobre todas las estrat, Elevada eficiència tèrmica i mínimes emissions contaminants impostes per les normatives anticontaminants en motores alternatius representen el principal objectiu dels fabricants de motors. La estratègia de combustió diésel convencional es àmpliament utilitzada per tot el mon gracies al excel·lent consum de carburant. Esta estratègia permet operar el motor amb dosatges pobres que resulten en elevada eficiència tèrmica. A més, aquest tipus de combustió pot ser aplicada tant a els motor mes lleugers con als motor per aplicacions marines. No obstant això, aquest procés de combustió implica la generació de elevats nivells de emissió de NOx i sutja, que no es poden reduir simultàniament. Per tant, els fabricants han incorporat sistemes de post-tractament amb el objectiu de acomplir les normatives anticontaminació, que pretenen obtindre motors en emissions mes netes i mes eficients. Per el contrari, aquest tipus de sistemes per a reduir les emissions incrementen la complexitat del motor i els costos tant de producció com operatius al llarg del cicle de vida del motor. La comunitat científica continua desenvolupant solucions alternatives a la combustió dièsel mantenint els beneficis d¿aquest tipus de combustió però reduint les emissions (principalment NOx i sutja). La comunitat científica ha trobat a les estratègies de combustió de baixa temperatura un procés de combustió que te elevada eficiència tèrmica i extremadament baixes emissions de NOx y partícules. En aquest sentit, la revisió bibliogràfica constata que aquests tipus de combustions permeten la reducció simultània dels contaminants NOx i sutja, trencant el tradicional "trade-off" existent a la combustió dièsel. De entre totes les estratègies proposades de baixa temperatura, la estratègia combustió dominada per la reactivitat del combustible presenta mes potencial que les altres. Aquest procés de combustió es caracteritza per utilitzar dos combustibles, lo que li permet solventar els principals problemes que han apa, High thermal efficiency coupled to minimum pollutants emissions imposed by the stringent standard emissions limitations in reciprocating engines represent the main target of the engine manufacturers industry. Conventional diesel combustion strategy is widely used worldwide due to its excellent fuel economy. This combustion strategy allows operating under lean mixtures of fuel and air that provide high thermal efficiency. In addition, this type of combustion can be applied from light-duty engines to large bore marine engines. However, the combustion process leads to high NOx and particle matter emissions, being impossible to reduce both pollutants simultaneously. Hence, manufactures have incorporated aftertreatment systems in order to meet the imposed standard emissions limitations, which are aimed to provide cleaner emissions and high efficiency. By contrast, these systems required for the emissions mitigation result in a very complex processes and an increase in the engine production and operational costs. The research community continues developing alternative solutions to the conventional diesel combustion concept keeping the benefits of this combustion process while the emissions are reduced (mainly focused on NOx and soot). Research community have found in the low temperature combustion strategies the combustion process able to provide excellent high thermal efficiency and ultra-low NOx and smoke emissions. In this sense, the literature review states that this types of combustion processes allow the simultaneous reduction of NOx and smoke, breaking the traditional trade-off found in diesel engines. Amongst others, the most promising strategy is the reactivity controlled compression ignition. This combustion process is characterized by using two fuels and is able to solve the main challenges of the low temperature combustion processes such as combustion phasing control. Nonetheless, the reactivity controlled strategy also presents some challenges such as excessi

[EN] This work investigates the particulates size distribution of reactivity controlled compression ignition combustion, a dual-fuel concept which combines the port fuel injection of low-reactive/gasoline-like fuels with direct injection of highly reactive/diesel-like fuels. The particulates size distributions from 5-250 nm were measured using a scanning mobility particle sizer at six engine speeds, from 950 to 2200 rpm, and 25% engine load. The same procedure was followed for conventional diesel combustion. The study was performed in a single-cylinder engine derived from a stock medium-duty multi-cylinder diesel engine of 15.3:1 compression ratio. The combustion strategy proposed during the tests campaign was limited to accomplish both mechanical and emissions constraints. The results confirms that reactivity controlled compression ignition promotes ultra-low levels of nitrogen oxides and smoke emissions in the points tested. However, in spite of having similar or lower smoke emissions, the number of particles in some conditions is higher for the reactivity controlled compression ignition than for conventional diesel combustion. Nucleation mode dominates the particle formation for the reactivity controlled compression ignition mode, while accumulation mode dominates the particle formation for conventional diesel combustion. Thus, it is confirmed that the smoke measurement in filter smoke number units cannot be used to correlate the total particle mass for the reactivity controlled compression ignition mode, as typically done for conventional diesel combustion.

[EN] Low temperature combustion concepts are in focus of study nowadays as a method to avoid the NOx-soot trade-off existing with conventional diesel combustion. One of the most promising strategy is known as reactivity controlled compression ignition because of its high thermal efficiency and the ultra-low nitrogen oxides and soot emissions. However, this concept presents several challenges such as the high levels of carbon monoxide and unburned hydrocarbons promoted at low load and unacceptable levels of pressure rise rate at high load. Therefore, to mitigate these shortcomings the dual-mode dual-fuel concept, combining reactivity controlled compression ignition and diffusive dual-fuel diesel-gasoline combustion, has been developed. Total number of particles is also limited by the emission standards. Previous studies focused in particles emissions carried out by the research community present particle size distribution, composition and mass of the particles on reactivity controlled compression ignition combustion mode. Additional studies were carried out in order to identify the components of these particles, being partially formed of volatiles, and reflects that particles are smaller than at conventional diesel combustion, presenting higher number of particles from nucleation mode than from accumulation mode. Dual-Mode Dual-Fuel concept may present a different behavior for particle distribution with respect to the conventional diesel combustion or the traditional low temperature concepts due to the nature of the particles. The objective of the present study is to measure the particle size distribution as well as gaseous emissions of this new Dual-Mode Dual-Fuel concept from low load to full load for a representative engine speed of 1200 rpm. Main results of this study suggest that Dual-Mode Dual-Fuel concept promotes higher quantity of particles than conventional diesel combustion despite of providing less smoke. In addition, nucleation mode particles dominate th

[EN] Literature demonstrates that, for premixed low temperature combustion concepts, particulate matter cannot be directly extrapolated from soot emissions measurements, as typically done for conventional diesel combustion. This is because the particulate matter from low temperature combustion has low fraction of carbonaceous compounds and great amount of soluble organic fraction, which is not captured by the smoke measurement techniques such as the optical reflectometry. By this reason, the study of the particulate matter characteristics from this combustion techniques requires using specific equipment. The aim of the current work is to gain understanding on the particulate matter characteristics from the dual-mode dual-fuel combustion, which is an optimized combustion strategy that combines fully and highly premixed RCCI regimes at low and medium loads, and switches to dual-fuel diffusion combustion at full load. The study was performed over the whole engine map, using a 15.3:1 compression ratio medium-duty EURO VI diesel engine. In particular, the particulate number and size distributions were sampled using a scanning mobility particle sizer and a condensation particle counter, which allow measuring the size distribution and total number of particles from 5 to 250 nm. Results demonstrate that the fully premixed RCCI combustion is dominated by small particles (less than 30 nm in mobility diameter), the dual-fuel diffusion mode is dominated by larger particles (around 100 nm in mobility diameter) showing more diesel-like particle size distributions, and the highly premixed reactivity controlled compression ignition regime shows a transitional particle size distribution with two peaks of mobility diameters around 20 and 80 nm. (C) 2017 Elsevier Ltd. All rights reserved.

[EN] Stringent emissions limits introduced for internal combustion engines impose a major challenge for the research community. The technological solution adopted by the manufactures of diesel engines to meet the NOx and particle matter values imposed in the EURO VI regulation relies on using selective catalytic reduction and particulate filter systems, which increases the complexity and cost of the engine. Alternatively, several new combustion modes aimed at avoiding the formation of these two pollutants by promoting low temperature combustion reactions, are the focus of study nowadays. Among these new concepts, the dual-fuel combustion mode known as reactivity controlled compression ignition (RCCI) seems more promising because it allows better control of the combustion process by means of modulating the fuel reactivity depending on the engine operating conditions. The present experimental work explores the potential of different strategies for reducing the energy losses with RCCI in a single-cylinder research engine, with the final goal of providing the guidelines to define an efficient dual-fuel combustion system. The results demonstrate that the engine settings combination, piston geometry modification, and fuel properties variation are good methods to increase the RCCI efficiency while maintaining ultra-low NOx and soot emissions for a wide range of operating conditions.

[EN] This experimental work investigates the capabilities of the reactivity controlled compression ignition combustion concept to be operated in the whole engine map and discusses its benefits when compared to conventional diesel combustion. The experiments were conducted using a single-cylinder medium duty diesel engine fueled with regular gasoline and diesel fuels. The main modification on the stock engine architecture was the addition of a port fuel injector in the intake manifold. In addition, with the aim of extending the reactivity controlled compression ignition operating range towards higher loads, the piston bowl volume was increased to reduce the compression ratio of the engine from 17.5:1 (stock) down to 15.3:1. To allow the dual-fuel operation over the whole engine map without exceeding the mechanical limitations of the engine, an optimized dual-fuel combustion strategy is proposed in this research. The combustion strategy changes as the engine load increases, starting from a fully premixed reactivity controlled compression ignition combustion up to around 8 bar IMEP, then switching to a highly premixed reactivity controlled compression ignition combustion up to 15 bar IMEP, and finally moving to a mainly diffusive dual-fuel combustion to reach the full load operation. The engine mapping results obtained using this combustion strategy show that reactivity controlled compression ignition combustion allows fulfilling the EURO VI NOx limit up to 14 bar IMEP. Ultra-low soot emissions are also achieved when the fully premixed combustion is promoted, however, the soot levels rise notably as the combustion strategy moves to a less premixed pattern. Finally, the direct comparison of reactivity controlled compression ignition versus conventional diesel combustion using the nominal engine settings, reveals that reactivity controlled compression ignition can be a potential solution to reduce the selective catalyst reduction and diesel particulate filter aftertreatm

[EN] The present paper addresses the optimal heat release (HR) law in a single cylinder engine operated under reactivity controlled compression ignition (RCCI) combustion mode to minimise the indicated specific fuel consumption (ISFC) subject to different constraints including pressure related limits (maximum cylinder pressure and maximum cylinder pressure gradient). With this aim, a 0-dimensional (0D) engine combustion model has been identified with experimental data. Then, the optimal control problem of minimising the ISFC of the engine at different operating conditions of the engine operating map has been stated and analytically solved. To evaluate the method viability a data-driven model is developed to obtain the control actions (gasoline fraction) leading to the calculated optimal HR, more precisely to the optimal ratio between premixed and diffusive combustion. The experimental results obtained with such controls and the differences with the optimal HR are finally explained and discussed.

Reactivity controlled compression ignition (RCCI) concept offers ultra-low NOx and smoke emissions with a thermal efficiency. The present work investigates the capabilities of this new Low Temperature Combustion (LTC) concept on the whole engine map of a medium-duty engine proposing strategies to solve its main challenges. Therefore, in order to extent the engine operation up to full load, several constraints must be accomplished. These constraints are summarized in two groups: Mechanical constraints: ¿ Maximum pressure rise rate <15bar/CAD ¿ In-cylinder pressure < 190 bar Emissions constraints: ¿ NOx emissions <0.4 g/kWh ¿ Smoke emissions < 1.5 FSN Despite of not having any specific constraint regarding carbón monoxide (CO) and unburned hydrocarbons (HC), during the tests these emissions have been taken in account to control them due to the high quantity of CO and uHC emissions promoted by this concept. From the tests standpoint, the experiments of this investigation were carried out in a single-cylinder engine (SCE) derived from a commercial medium-duty four cylinders engine which is able to meet EURO VI limitation standard. A SCE is required in this kind of investigation due to the precise control of the variables which take part in the combustion process. Additional modifications were performed in the SCE with the aim to improve the engine conditions to apply the RCCI concept. In this sense, different compressions ratios (CR) were tested apart from the stock configuration (CR12.75 and CR15.3). RCCI concept requires two different reactivity fuels. Therefore, gasoline 95 RON (EN228) was used as the low reactivity fuel and diesel (EN 590) was used as a high reactivity fuel. These fuels were chosen due to they can be obtained in any petrol station and thereby, it is possible to implement this LTC concept with conventional fuels. Regarding the fuel injection systems, a double injection system was developed to manage the injection of both fuels independently. In this, El modo de combustion reactivity controlled compression ignition (RCCI) produce emisiones de óxidos de nitrógeno (NOx) y humo sumamente reducidas con respecto al diésel convencional mientras que es capaz de mantener o superar su eficiencia térmica. Éste trabajo estudia las capacidades potenciales de este nuevo concepto de combustión de baja temperatura (LTC- Low Temperature Combustion) para ser extrapolado a todo el rango de operación de un motor médium-duty de combustión interna. Para ello, se han investigado diversas configuraciones de motor con la intención de superar los posibles inconvenientes de este tipo de modo de combustión y así poder alcanzar los objetivos de la investigación. Adicionalmente, se han de cumplir una serie de restricciones: Restricciones mecánicas: ¿ Gradiente de presión <15bar/CAD ¿ Presión en el cilindro < 190 bar Restricciones en emisiones: ¿ Emisiones de óxidos de nitrógeno <0.4 g/kWh ¿ Emisiones de humo < 1.5 FSN Por otro lado, se ha tenido en cuenta las emisiones de monóxido de carbono (CO) e hidrocarburos (HC) inquemados, especialmente elevados en este tipo de combustión y que no son foco del principal interés de este estudio. Para realizar este trabajo, se han llevado a cabo una serie de ensayos en un motor monocilíndrico derivado de un motor de 4 cilindros médium-duty de producción en serie. El uso de un motor monocilíndrico es necesario para poder obtener un control preciso del proceso de combustión. Para poder emplear este modo de combustión en el motor, se han probado diferentes relaciones de compresión (RC), la original de 17,5 y dos modificadas de 12,75 y 15,3. El concepto de combustión RCCI requiere el uso de combustibles con diferente reactividad. Con el fin de disponer de las condiciones más reales posibles, se ha optado por gasolina 95 RON (EN 228) como combustible de baja reactividad y diésel (EN 590) como combustible de alta reactividad, combustibles que son muy fáciles de adquirir en cualquier estación de servicio. Para

Reactivity Controlled Compression Ignition concept offers an ultra-low nitrogen oxide and soot emissions with a high thermal efficiency. This work investigates the capabilities of this low temperature combustion concept to work on the whole map of a medium duty engine proposing strategies to solve its main challenges. In this sense, an extension to high loads of the concept without exceeding mechanical stress as well as a mitigation of carbon oxide and unburned hydrocarbons emissions at low load together with a fuel consumption penalty have been identified as main Reactivity Controlled Compression Ignition drawbacks. For this purpose, a single cylinder engine derived from commercial four cylinders medium-duty engine with an adapted compression ratio of 12.75 is used. Commercial 95 octane gasoline was used as a low reactivity fuel and commercial diesel as a high reactivity fuel. Thus, the study consists of two different parts. Firstly, the work is focused on the development and evaluation of an engine map trying to achieve the maximum possible load without exceeding a pressure rise rate of 15 bar/CAD. The second part holds on improving fuel consumption and carbon oxide and unburned hydrocarbons emissions at low load. Results suggest that it is possible to achieve up to 80% of nominal conventional diesel combustion engine load without overpassing the constraints of pressure rise rate (below 15 bar/CAD) and maximum pressure peak (below 190 bar) while obtaining ultra-low levels of nitrogen oxide and soot emissions. Regarding low load challenges, it has developed a particular methodology sweeping the gasoline-diesel blend together with intake temperature or exhaust gas recirculation maintaining constant the combustion phasing and ultra-low nitrogen oxide and soot emissions. As a result a drastic decrease carbon oxide and unburned hydrocarbons emissions is obtained with a slight fuel consumption improvement.

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