**Dual-Fuel Combustion for Future Clean and Efficient Compression Ignition Engines**

### **Jesús Benajes, Antonio García \*, Javier Monsalve-Serrano and Vicente Boronat**

CMT-Motores Térmicos, Universitat Politècnica de València, Camino de Vera s/n, Valencia 46022, Spain; jbenajes@mot.upv.es (J.B.); jamonse1@mot.upv.es (J.M.-S.); viboco1@mot.upv.es (V.B.)

**\*** Correspondence: angarma8@mot.upv.es; Tel.: +34-963-877-659

Academic Editor: Jose Ramon Serrano

Received: 24 November 2016; Accepted: 23 December 2016; Published: 29 December 2016

**Abstract:** 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.

**Keywords:** reactivity controlled compression ignition; efficiency; EURO VI emissions; dual-fuel
