Catalytic Exhaust Gas Recirculation-Loop Reforming for High Efficiency in a Stoichiometric Spark-Ignited Engine through Thermochemical Recuperation and Dilution Limit Extension, Part 1: Catalyst Performance

Abstract

The use of fuel reformate from catalytic processes is known to have beneficial effects on the spark-ignited combustion process through enhanced dilution tolerance and decreased combustion duration, but, in many cases, reformate generation can incur a significant fuel penalty. In this two-part investigation, we demonstrate that efficient catalytic fuel reforming can result in improved brake engine efficiency while maintaining stoichiometric exhaust under the right conditions. In Part 1 of this investigation, we used a combination of thermodynamic equilibrium calculations and experimental fuel catalytic reforming measurements on an engine to characterize the best possible reforming performance and energetics over a range of equivalence ratios and O2 concentrations. Ideally, one might expect the highest levels of thermochemical recuperation for the highest catalyst equivalence ratios. However, reforming under these conditions is highly endothermic, and the available enthalpy for reforming is constrained. Thus, for relatively high equivalence ratios, more methane and less H2 and CO are produced. Our experiments revealed that this suppression of H2 and CO could be countered by adding small amounts of O2, yielding as much as 15 vol % H2 at the catalyst outlet for 4 < Φcatalyst < 7 under quasi-steady-state conditions. Under these conditions, the H2 and CO yields were highest and there was significant water consumption, confirming the presence of steam reforming reactions. Analyses of the experimental catalyst measurements indicated the possibility of both endothermic and exothermic reaction stages and global reaction rates sufficient to enable the utilization of higher space velocities than those employed in our experiments. In a companion paper detailing Part 2 of this investigation, we present results for the engine dilution tolerance and brake engine efficiency impacts of the reforming levels achieved.

Catalytic Exhaust Gas Recirculation-Loop Reforming for High Efficiency in a Stoichiometric Spark-Ignited Engine through Thermochemical Recuperation and Dilution Limit Extension, Part 2: Engine Performance

“…H 2 concentration as a function of oxygen catalyst flow and Φ catalyst at the catalyst inlet for (a) catalyst-out concentration from the catalyst mapping study and (b) intake manifold concentration for the multicylinder experiments.…”

“…In the companion paper (Part 1, "Catalyst Performance"), we reported on the reformer catalyst performance over a range of Φ catalyst conditions in an effort to find a balance between the POx activity required for catalyst durability and the endothermic steam reforming reactions required to minimize energy losses or to achieve TCR during reforming. 48 In this paper, we characterize the multicylinder engine performance while maintaining stoichiometric exhaust emissions with the EGR-loop reforming strategy, focusing on whole-engine performance, including dilution tolerance, combustion performance, and brake thermal efficiency.…”

Catalytic Steam and Partial Oxidation Reforming of Liquid Fuels for Application in Improving the Efficiency of Internal Combustion Engines

“…Overall, it was found that partial oxidation reforming of liquid fuels in a simulated EGR mixture over the Rh/Al 2 O 3 catalyst demonstrated sufficiently high reformate yields and favorable energetics to warrant further evaluation in the EGR system of a stoichiometric combustion engine. 49,50 The net impact of EGR loop reforming on engine efficiency will be dependent on EGR gas temperature and composition as well as fuel properties. Future studies will investigate the durability of this process.…”

Exploring the potential of reformed-exhaust gas recirculation (R-EGR) for increased efficiency of methanol fueled SI engines

“…The direct contact is preferred because it provides a better heat transfer and the combustion products can be used as an additional reactant. The hot gas is the EGR mixture (reformed-EGR concept) [30], or is the exhaust of one cylinder [31,32]. In the first one, the fuel is injected into the EGR loop, upstream the catalyst and reacted with water vapor and/or CO 2 in the exhaust over the catalyst to produce syngas (see Figure 1).…”

“…The additional fuel injects at the end of the expansion stroke, to provide a fuel rich mixture (with oxygen left from the combustion) and feed it into the catalyst during the exhaust stroke. [31] which is located inside the exhaust system of that cylinder. The products then recirculate back to the intake to mix with the air of the other cylinders.…”