On-board hydrogen and syngas production is considered as a transition solution from fossil fuel to hydrogen powered vehicles until problems associated with hydrogen infrastructure, distribution and storage are resolved. A hydrogen- or syngas-rich stream, which substitutes part of the main hydrocarbon fuel, can be produced by supplying diesel fuel in a fuel-reforming reactor, integrated within the exhaust pipe of a diesel engine. The primary aim of this project was to investigate the effects of intake air enrichment with product gas on the performance, combustion and emissions of a diesel engine. The novelty of this study was the utilisation of the dilution effect of the reformate, combined with replacement of part of the hydrocarbon fuel in the engine cylinder by either hydrogen or syngas. The experiments were performed using a fully instrumented, prototype 2.0 litre Ford HSDI diesel engine. The engine was tested in four different operating conditions, representative for light- and medium-duty diesel engines. The product gas was simulated by bottled gases, the composition of which resembled that of typical diesel reformer product gas. In each operating condition, the percentage of the bottled gases and the start of diesel injection were varied in order to find the optimum operating points. The results showed that when the intake air was enriched with hydrogen, smoke and CO emissions decreased at the expense of NOx. Supply of nitrogen-rich combustion air into the engine resulted in a reduction in NOx emissions; nevertheless, this technique had a detrimental effect on smoke and CO emissions. Under low-speed low-load operation, enrichment of the intake air with a mixture of hydrogen and nitrogen led to simultaneous reductions in NOx, smoke and CO emissions. Introduction of a mixture of syngas and nitrogen into the engine resulted in simultaneous reductions in NOx and smoke emissions over a wide range of the engine operating window. Admission of bottled gases into the engine had a negative impact on brake thermal efficiency. Although there are many papers in the literature dealing with the effects of intake air enrichment with separate hydrogen, syngas and nitrogen, no studies were found examining how a mixture composed of hydrogen and nitrogen or syngas and nitrogen would affect a diesel engine. Apart from making a significant contribution to existing knowledge, it is 3 believed that this research work will benefit the development of an engine-reformer system since the product gas is mainly composed of either a mixture of hydrogen and nitrogen or a mixture of syngas and nitrogen.

This study presents a detailed gas-phase and surface kinetic model for n-tetradecane autothermal reforming to deconvolute the complex reaction network that provides the mechanistic understanding of reforming chemistry in a packed-bed reactor. A thermodynamic analysis study for diesel reforming was performed to map the carbon formation boundary for various reforming processes. Through a Langmuir-Hinshelwood-Hougen-Watson (LHHW) type of kinetic model, which was derived using a simple mechanistic study, the need for a detailed kinetic study including both gas-phase reactions and surface reactions was identified. Pt-CGO (Pt on Gd doped CeO2) and Rh-pyrochlore catalysts were synthesized and characterized. In an accelerated test for reforming of commercial-diesel, Rh-pyrochlore catalyst showed stable performance for 24 hrs, whereas Pt-CGO catalyst deteriorated in 4 hrs. Minimum structural change in Rh-pyrochlore catalyst compared to Pt-CGO catalyst was observed using redox experiments. An experimental kinetic study with an inert silica bed provided clear evidence that the gas-phase reactions are important to the kinetics of hydrocarbon reforming. “Reaction Mechanism Generator” (RMG) software was employed to generate a detailed gas-phase kinetic model containing nine thousand three hundred and forty-seven elementary reactions and four hundred and fifty-nine species. The model was validated against n-tetradecane ignition delay data, and inert bed autothermal reforming data. The RMG model was also extended to capture the high pressure and low temperature pyrolysis chemistry to predict pyrolysis experimental data. The reactor simulation using the RMG model identified the detailed chemistry of the reactions in the pre-catalytic zone. Gas-phase oxidation/pyrolysis converts the heavier hydrocarbons and oxygen in the pre-catalytic zone to lower molecular weight products prior to reaching the catalyst surface. The steam reforming reactions that are dominant on the surface of the catalyst primarily involve lower molecular weight oxidation/pyrolysis products. A multi-component micro-kinetic model containing two hundred and seventy surface reactions and fifty-two adspecies was developed using a semi-empirical Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. Transition State Theory estimates were used for elementary reactions up to C3 species, and simple fragmentation reactions were assumed for higher hydrocarbon species. Model simulations indicated on the catalyst surface that hydrogen is initially produced by the water-gas-shift reaction and subsequently by steam reforming reactions. A major reaction path for ethylene formation from 1,3 butadiene in the post-catalytic zone of the reactor was also identified. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-04-24 13:23:31.163