An HCCI combustion engine system using on-board reformed gases of methanol with waste heat recovery: ignition control by hydrogen

Abstract

Adjusting a proportion of two fuels with different ignition properties is an effective technique for controlling the ignition timing in HCCI combustion. This research newly proposes an HCCI combustion engine system fuelled with dimethyl ether (DME) having a high cetane number and methanol-reformed gas (MRG) having a high anti-knock property. In the system, both DME and MRG are to be produced from methanol by onboard reformers utilising the exhaust heat from the engine. Because the reactions producing DME and MRG are endothermic, a part of exhaust heat energy can be recovered during the fuel reforming process. This research experimentally investigated characteristics of combustion, exhaust emissions, engine efficiency and overall thermal efficiency including the waste heat recovery through the fuel reforming in the HCCI combustion engine system. Because MRG consists of hydrogen and carbon monoxide, effects of the two on the autoignition of DME were also analysed.Keywords: DME; HCCI; hydrogen; ignition control; methanol; on-board reforming; waste heat recovery.Reference to this paper should be made as follows: Shudo, T. IntroductionIt is expected that the use of homogeneous charge compression ignition (HCCI) combustion in internal combustion engines will result in the higher thermal efficiency and the lower NOx emission as compared with conventional combustion systems. However, the difficulty in controlling the ignition timing in accordance with the engine load is preventing the HCCI combustion from its practical application to vehicles. Adjusting the proportion of two fuels with different ignition properties has been reported as a technique to control the ignition timing and load in HCCI combustion [1,2]. However, this technique has not been practically used for vehicles because of the obvious inconvenience of carrying two kinds of fuels onboard. On the other hand, dimethyl ether (DME) has been studied as a clean alternative to the diesel fuel due to its high cetane number and smokeless combustion [3][4][5]. DME can be easily produced from methanol by the dehydration reaction [6]. There has been reported an idea to use a small amount of DME that was produced from methanol as an ignition improving agent in a methanol direct-injection diesel engine [3]. Methanol also can be thermally decomposed to methanol-reformed gas (MRG) that consists of hydrogen and carbon monoxide. Since both hydrogen and carbon monoxide have high anti-knock properties [7], MRG has been studied as a fuel for spark-ignition engines [8,9]. For this background, the author newly proposes an HCCI combustion engine system that is fuelled with DME and MRG. Because the ignition properties of DME and MRG are largely different, adjusting the proportion of the two fuels could control the ignition timing in the HCCI combustion engine fuelled with them. In addition to the ignition control, the author also proposes productions of DME and MRG by onboard methanol reformers utilising the exhaust gas heat of the HCCI engine as shown in Figure 1. Bec...

Chemical kinetics and CFD analysis of supercharged micro-pilot ignited dual-fuel engine combustion of syngas

“…Varying proportions of H 2 , CO, CH 4 , CO 2 , H 2 O, and N 2 may be present [2]. Mixtures of H 2 and CO have high antiknock behaviour and therefore could serve as fuels for internal combustion engines [3,4]. However, the addition of hydrogen to carbon monoxide or methane tends to increase combustion temperatures and NOx emissions under stoichiometric conditions [5].…”

Investigating various effects of reformer gas enrichment on a natural gas-fueled HCCI combustion engine

“…Shudo et al examined the effect of variable blend fractions of methanol reformer gas (MRG) and DME [14,15]. Eng et al in an experimental chemical kinetics modeling study examined the effects of PO x RG on HCCI combustion of n-heptane and iso-octane with two strategies of internal EGR through exhaust re-breathing and external well-mixed EGR [16].…”

Waste Heat Recycling for Fuel Reforming

“…Because the reactions producing DME and MRG are endothermic, a part of exhaust heat energy can be recovered during the fuel reforming process. This research experimentally investigated characteristics of combustion, exhaust emissions, engine efficiency and overall thermal efficiency including the waste heat recovery through the fuel reforming in the HCCI combustion engine system (Shudo, 2006). Tri-reforming of natural gas using flue gas from power plants with the combination of heat transfer or heat exchange including reactor heat up and waste heat utilization was studied.…”