Premixed combustion of GTL and RME fuels in a single cylinder research engine Ezio Mancaruso ⇑ , Bianca Maria Vaglieco Istituto Motori, Consiglio Nazionale delle Ricerche, Via G. Marconi, 8, 80125 Naples, Italy article info Article history: Received 11 March 2011 Received in revised form 29 August 2011 Accepted 8 October 2011 Available online 5 November 2011 Keywords: Biodiesel Premixed combustion Optical diagnostics UV–Visible digital imaging abstract In this paper we report the use of the optical technique applied in the cylinder of an optically accessible engine equipped with the latest-generation diesel engine head of a European passenger car. The injection strategy with high percentage of EGR, characteristic of real engine operating point, was adopted. Alterna- tive diesel fuels were used. In particular, rapeseed methyl ester (RME) and gas to liquid (GTL) were selected as representative of 1st and 2nd generation alternative diesel fuels, respectively. Combustion analysis was carried out in the engine combustion chamber by means of 2D spectroscopic measurements from UV to visible. These measurements helped to analyze the chemical and physical events occurring during the mixture preparation and the combustion development. Ultraviolet (UV) digital imaging was also performed and the presence of characteristic radical, like OH, in the various phases of combustion was detected as well. OH spatial distribution and temporal evolution were measured. Two color pyrom- etry technique was applied in order to measure the soot volume fraction within the combustion chamber. The GTL fuel showed better performance in terms of indicated mean effective pressure (IMEP) with respect to the diesel reference fuel with different effects on particulate matter (PM) and gaseous emis- sions. It showed the highest in cylinder soot production, while the OH radical had maximum intensity value close to the reference diesel (REF) one. On the other hand, the RME fuel showed a decrease in IMEP that can be adjusted with a little increase of fuel injected quantity, and very low production of soot in the cylinder and PM at the exhaust compared to the diesel reference fuel. Finally, the OH radical had the low- est intensity value. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The reduction of CO 2 emissions from vehicles is one of the main targets for the future development of internal combustion engines. In order to achieve this target, the research on compression ignition engines is working on the reduction of compression ratio as well as the use of biofuels. In particular, in Europe the last diesel engine managed by electronic control unit can work with several combus- tion modes. The engine has a lower compression ratio compared to the previous versions and it can run with highly premixed combus- tion using the maps stored in the electronic control unit (ECU). Moreover, the use of the low-temperature combustion was achieved by using a high EGR rate, up to 60%, with a reduced in-cylinder oxy- gen concentration, and the sufficient mixing time was attained by prolonging the ignition delay as well as promoting the dispersion of injected fuel [1,2]. From an environmental point of view, the use of biofuels can contribute to a significant reduction of greenhouse gas (GHG) emissions [3–5]. Within this framework, biofuel produc- ers and OEMs are jointly devoting significant efforts in optimizing benefits from 1st generation biofuels while making 2nd generation technologies economically viable soon. The first generation biodie- sel designates a wide range of methyl ester blends produced from vegetable oils and animal fats through a thermo-chemical process involving methanol (transesterification) that features both high en- ergy conversion efficiency and fuel yield from processed oil [6]. More recently, starting from the well-known Fischer–Tropsch synthesis process, which is able to produce liquid fuels from the so-called syn- gas (a mixture of H 2 , CO, CO 2 ,H 2 O as well as other compounds), a 2nd generation of alternative diesel fuels were developed. It is usually indicated with xTL, where x denotes the specific source feedstock 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.10.010 Abbreviations: ATDC, after top dead center; BMEP, brake mean effective pressure; BSFC, brake specific fuel consumption; BTDC, before top dead center; CAD, crank angle degree; CCD, coupled charge device; CN, cetane number; CO, carbon monoxide; CO 2 , carbon dioxide; CR, Common Rail injection system; DPF, diesel particulate filter; DeNO x , de nitrogen oxide; ECU, electronic control unit; EGR, exhaust gas recirculation; ET, energizing time; FAME, fatty-acid-methyl- esters; GHG, greenhouse gas; GTL, gas-to-liquid; HC, unburned hydrocarbons; IMEP, indicated mean effective pressure; ICCD, intensified coupled charge device; IR, infrared; LHV, lower heating value of fuel; NEDC, new European driving cycle; NO x , nitrogen oxides; P inj , injection pressure (measured in the rail); PM, partic- ulate matter; REF, reference diesel fuel; RME, rapeseed methyl-ester; ROHR, rate of heat release; SOC, start of combustion; TDC, top dead center; UV, ultraviolet; VSA, variable swirl throttle actuator. ⇑ Corresponding author. Tel.: +39 081 7177187; fax: +39 081 2396097. E-mail address: e.mancaruso@im.cnr.it (E. Mancaruso). Applied Energy 91 (2012) 385–394 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy