Optical investigation of the combustion behaviour inside the engine operating in HCCI mode and using alternative diesel fuel E. Mancaruso * , B.M. Vaglieco Istituto Motori – CNR, Via Marconi, 8, 80125 Napoli, Italy article info Article history: Received 13 October 2009 Accepted 16 October 2009 Keywords: Optical diagnostics HCCI combustion Rape seed methyl ester abstract In order to understand the effect of both the new homogeneous charge compression ignition (HCCI) com- bustion process and the use of biofuel, optical measurements were carried out into a transparent CR die- sel engine. Rape seed methyl ester was used and tests with several injection pressures were performed. OH and HCO radical were detected and their evolutions were analyzed during the whole combustion. Moreover, soot concentration was measured by means the two colour pyrometry method. The reduction of particulate emission with biodiesel as compared to the diesel fuel was noted. Moreover, this effect resulted higher increasing the injection pressure. In the case of RME the oxidation of soot depends mainly from O 2 content of fuel and OH is responsible of the NO formation in the chamber as it was observed for NO x exhaust emission. Moreover, it was investigated the evolution of HCO and CO into the cylinder. HCO was detected at the start of combustion. During the combustion, HCO oxidizes due to the increasing tem- perature and it produces CO. Both fuels have similar trend, the highest concentrations are detected for low injection pressure. This effect is more evident for the RME fuel. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction The growing transport sector is considered to be one of the main reasons for failing to meet the Kyoto targets. In combination with the emission limits and new emission standards, the already very low CO 2 emission levels have to be further reduced both for spark ignition and diesel engines. Particularly, in Europe the trans- port sector accounts for more than 30% of the total energy con- sumption in the Community. It is 98% dependent on fossil fuels with the crude oil feedstock being largely imported and thus extre- mely vulnerable to any market disturbance. Biofuel use has to in- crease from its present low usage – less than 2% of overall fuel – to a substantial fraction of the transportation fuel consumption in Europe (target of 25% in 2030). However, biofuels will mostly be used in compressed ignition and spark engines and/or if it is possible specialized engines will be used in certain applications or in dedicated fleets. The most commonly known biofuels are eth- anol and biodiesel. Biodiesel is a renewable fuel that can be produced from a vari- ety of vegetable oils including rapeseed oil, soybean oil, sunflower oil and palm oil. Waste fryer oil, which is considered toxic waste by the Environmental Protection Agency (EPA), can also be transeste- rified into biodiesel. Rapeseed Methyl Ester (RME) is the more widely used in Europe and Soybean Methyl Ester (SME) or im- ported palm oil in the USA they are collectively known as Fatty Acid Methyl Esters (FAME). The benefits of the biodiesel–FAME are well known: higher cetane number, low sulphur content, reduction of HC and CO emission, reduction of PM emission. Even if the materials compatibility, the impact on low-temperature operability, the increase in NO x emission, the reduction of power and the fuel economy, and the higher cost of production must be evaluated [1–3]. In order to overcome these limitations and contribute further to the emission reduction, the use of homogeneous charge compres- sion ignition (HCCI) mode must be considered in direct injection diesel engine using biodiesel fuel because some future production engines will adopt this combustion mode. HCCI mode reduces PM and NO x emissions without penalize the performances. This occurs because the combustion develops with low temperature and burns a premixed air/fuel mixture. On the other hand, CO and HC emissions increase because the low temperature doesn’t favour their complete reduction in the cylinder. Another limit is the autoignition that remains a process not usually perfect causing knock phenomena [4–7]. The combustion process and the pollu- tants formation depend on the compression ratio, the quality of 0894-1777/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.expthermflusci.2009.10.010 Abbreviation: ATDC, after top dead centre; BTDC, before top dead centre; CAD, crank angle degree; DI, direct injection; DT, dwell time; ECE, United Nations Economic Commission for Europe; EUDC, extra urban driving cycle; ET, energising timing; PM, particulate matter; PSOC, pressure start of combustion; SOC, start of combustion; SOI, start of injection; TDC, top dead centre; UV, ultraviolet. * Corresponding author. Address: Istituto Motori – Consiglio Nazionale delle Ricerche, Viale Marconi 8, 80125 Naples, Italy. Tel.: +39 081 7177187; fax: +39 081 2396097. E-mail address: e.mancaruso@im.cnr.it (E. Mancaruso). Experimental Thermal and Fluid Science 34 (2010) 346–351 Contents lists available at ScienceDirect Experimental Thermal and Fluid Science journal homepage: www.elsevier.com/locate/etfs