International Journal of Hydrogen Energy 32 (2007) 3565 – 3571 www.elsevier.com/locate/ijhydene The influence of H 2 and CO on diesel engine combustion characteristics, exhaust gas emissions, and after treatment selective catalytic NO x reduction A. Abu-Jrai a , A. Tsolakis a , ∗ , A. Megaritis b a School of Engineering, Mechanical and Manufacturing Engineering, University of Birmingham, Birmingham B15 2TT, UK b Mechanical Engineering, School of Engineering and Design, Brunel University, West London, Uxbridge UB8 3PH, UK Received 19 September 2006; received in revised form 16 February 2007; accepted 16 February 2007 Available online 3 April 2007 Abstract The requirement to significantly reduce NO x and particulate matter (PM) emissions while maintaining efficient combustion performance is one of the main drivers for internal combustion engine research. Modern diesel and premixed charge compression ignition (PCCI) engines have improved engine fuel economy and significantly reduced NO x and PM emissions achieved by advances in both combustion and exhaust aftertreatment technologies. To date, it has been shown that vehicle emissions can be further improved by several catalytic systems including fuel reformers (i.e. partial oxidation, autothermal, and exhaust gas reforming) and aftertreatment systems, such as the selective catalytic reduction (SCR) of NO x under oxygen-rich conditions. Among the most promising on-board reforming technologies is the exhaust-gas reforming, which allows the fuel/air feed to the engine to be enriched with reformate containing H 2 and CO. This method is a combination of reforming and exhaust-gas recirculation (EGR) and referred to as REGR. This paper reports on experimental results obtained when 1%Pt/Al 2 O 3 low temperature hydrocarbon-SCR catalyst was used to treat exhaust gas from a diesel engine operating with addition of simulated REGR (two different compositions). It has been shown that while REGR can directly improve engine performance and emissions by promoting the PCCI combustion mode, it can also benefit the performance of the SCR catalysts due to the presence of unburnt H 2 in the exhaust gas.  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Reforming; Hydrogen; REGR; HC-SCR; Platinum; Premixed combustion 1. Introduction While diesel engines are being considered to be attractive due to their high thermal efficiency and corresponding potential to minimize CO 2 emissions, concerns over health effects and air quality have promoted proposed reductions in diesel engine emissions, especially particulate matter (PM) and nitrogen ox- ides (NO x ). Hydrogen has been long believed to be one of the most promising alternative fuels for internal combustion engines from the point of emission control and engine performance. Hydrogen addition can be used in both compression and spark ignition engines to improve the fuel economy, combustion ∗ Corresponding author. Tel.: +44 121 414 4170; fax: +44 121 414 7484. E-mail address: a.tsolakis@bham.ac.uk (A. Tsolakis). 0360-3199/$ - see front matter  2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.02.014 stability, extend the engine tolerance to EGR and reduce the exhaust gas emissions [1–9]. Hydrogen’s low ignition energy limit and high burning rate make the hydrogen/hydrocarbon mixture easier to ignite, reducing misfires and thereby improv- ing emissions, performance and fuel economy [2–4]. Furthermore, hydrogen can be used advantageously in inter- nal combustion engines not only as an additive to hydrocarbon fuels, but also to improve the performance of the engine ex- haust gas aftertreatment devices such as selective catalytic re- duction (SCR) of NO x , NO x traps and diesel particulate filters (DPF) [e.g. 10,11]. SCR of NO x with hydrocarbons (HC-SCR) has the potential to eliminate NO x emissions from the oxygen-rich (lean condi- tions) exhaust. Since the early work of Iwamoto et al. [12] and Held et al. [13], a large number of different catalysts includ- ing alumina supported Pt have been proposed and tested for