Experimental Analysis of Diesel-Ignited Methane Dual-Fuel Low-Temperature Combustion in a Single-Cylinder Diesel Engine Mostafa S. Raihan 1 ; Edward S. Guerry 2 ; Umang Dwivedi 3 ; Kalyan Kumar Srinivasan 4 ; and Sundar Rajan Krishnan 5 Abstract: This paper focuses on the effect of diesel injection timing, intake boost pressure, and diesel injection pressure on diesel-methane dual-fuel combustion performed in a single-cylinder research engine. The engine was operated at a constant speed of 1,500 revolutions per minute (rpm) while percentage of methane energy substitution (PES) and load were maintained at 80% and 5.1 bar net indicated mean effective pressure (IMEP), respectively. The start of injection (SOI) of diesel was varied from 250 crank angle degrees (CAD) to 350 CAD while keeping the injection pressure at 500 bar and intake boost pressure at 1.5 bar. Advancing SOI from 330° to 300° reduced indicated specific NOx (ISNOx) emissions from 11.9 g=kW · h to less than 0.02 g=kW · h; further advancement of SOI did not yield any significant ISNOx reduction. Net indicated fuel conversion efficiency (IFCE) increases from 29.4% at 350 CAD SOI to 40.5% at 300 CAD SOI. Combustion efficiency trends are consistent with unburned hydrocarbon (HC) and carbon monoxide (CO) emission trends. Moreover, smoke emissions were lower than 0.1 filter smoke number (FSN) for all SOIs. A diesel injection pressure sweep from 200 to 1,300 bar at 300 CAD SOI showed that very low injection pressures lead to apparently more heterogeneous combustion and higher ISNOx, indicated specific CO (ISCO), and indicated specific HC (ISHC) emissions, whereas smoke, IFCE, and combustion efficiency remained unaffected. An injection pressure of approximately 500 bar appeared to be optimal for early SOIs. Finally, an intake boost pressure sweep from 1.1 to 1.8 bar at 300 CAD SOI and 500 bar injection pressure showed that ISNOx and smoke remained fairly low at all conditions (ISNOx < 0.15 g=kW · h; smoke < 0.1 FSN); however, increasing boost pressure resulted in an increase in both ISHC and ISCO emissions while combustion efficiency and IFCE were reduced. DOI: 10.1061/(ASCE)EY.1943-7897.0000235. © 2014 American Society of Civil Engineers. Author keywords: Low-temperature combustion; Dual-fuel combustion; Methane; NOx; Injection timing. Introduction Increasingly stringent exhaust emissions standards, the need for finding alternatives to liquid petroleum fuels, and the desire for higher fuel conversion efficiencies (FCEs) are key factors that have motivated research on advanced engine combustion strategies. Conventional diesel engines are constrained by tradeoffs between oxides of nitrogen (NOx) and particulate matter (PM) emissions. Current U.S. Environmental Protection Agency (USEPA) regula- tions for brake-specific PM and NOx emissions from heavy-duty diesel engines are 0.013 and 0.268 g=kW · h, respectively (Diesel- Net 2014). Simultaneous reduction of NOx and PM emissions without sacrificing fuel conversion efficiency (FCE) is an inherent challenge with conventional diesel combustion. In contrast, several low-temperature combustion (LTC) concepts that promise low NOx and PM have been investigated over the last decade (Dec 2009; Musculus et al. 2013). Alternatives to fossil-based fuels, in- cluding natural gas (Beck et al. 1997; Wong et al. 2000), propane (Goldsworthy 2012; Polk et al. 2014a), and biofuels from various sources (Agarwal 2007; Contino et al. 2013; Giakoumis et al. 2013; Lee et al. 2013; Sayin 2010) also have been considered. Although various biodiesel blends can be used in existing diesel engines without any hardware modifications, the NOx emissions are nor- mally higher with biodiesel operation (Giakoumis et al. 2013). In conventional diesel combustion, as described by Dec (1997), PM formation occurs in rich premixed combustion regions whereas NOx forms in the hot, near-stoichiometric mixtures of the diffusion flame surrounding the jet. Because NOx formation rates increase exponentially with temperature, in-cylinder NOx control strategies typically use exhaust gas recirculation (EGR) to reduce local temper- atures (Zheng et al. 2004). However, excessive EGR used with some LTC strategies can lead to poor combustion efficiencies (Huestis et al. 2007) because of the presence of high unburned hydrocarbon (HC) and carbon monoxide (CO) in the combustion products. To address the challenge of simultaneous NOx and PM re- duction in diesel engines, dual-fuel combustion has been investi- gated with a variety of alternative fuels, including natural gas, propane, and biogas (Gibson et al. 2011; Karim 2003; Krishnan et al. 2004; Kusaka et al. 2000; McTaggart-Cowan et al. 2006; 1 Graduate Student, Dept. of Mechanical Engineering, Mississippi State Univ., 210 Carpenter Building, Mississippi State, MS 39762. E-mail: mr1158@msstate.edu 2 Graduate Student, Dept. of Mechanical Engineering, Mississippi State Univ., 210 Carpenter Building, Mississippi State, MS 39762. E-mail: esguerry@gmail.com 3 Graduate Student, Dept. of Mechanical Engineering, Mississippi State Univ., 210 Carpenter Building, Mississippi State, MS 39762. E-mail: umang_dwivedi@yahoo.com 4 Associate Professor, Dept. of Mechanical Engineering, Mississippi State Univ., 210 Carpenter Building, Mississippi State, MS 39762. E-mail: srinivasan@me.msstate.edu 5 Associate Professor, Dept. of Mechanical Engineering, Mississippi State Univ., 210 Carpenter Building, Mississippi State, MS 39762 (corre- sponding author). E-mail: krishnan@me.msstate.edu Note. This manuscript was submitted on May 25, 2014; approved on August 1, 2014; published online on September 5, 2014. Discussion period open until February 5, 2015; separate discussions must be submitted for individual papers. This paper is part of the Journal of Energy Engineering, © ASCE, ISSN 0733-9402/C4014007(13)/$25.00. © ASCE C4014007-1 J. Energy Eng.