Abstract In this study we computationally investigate the effects of exhaust gas recirculation (EGR) and boosting to clarify the auto-ignition mechanisms of homogeneous charge compression ignition (HCCI) in natural-gas-fueled engines. CHEMKIN-PRO is used to perform the thermodynamic and chemical kinetics analysis. To set the boundaries of the operating range, intake air pressures are varied from naturally aspirated operation to boost pressure (0.3 MPa) and EGR ratios are varied from 0% to 50% at an equivalence ratio of φ = 0.4, intake air temperature of Tin = 430 K, and engine speed of 1200 rpm. Natural gas has a single stage heat release, which results in a high temperature heat release (HTHR). The HTHR is composed of two parts, the thermal ignition preparation and thermal ignition range, in which fuel series reactions, H2O2 loop reactions, and H2-O2 system reactions occur. The reaction paths and contribution ratios that occur within the transient temperature can be described by a contribution matrix. We found that when the EGR ratio is increased, auto-ignition is retarded with a longer duration of combustion. The absolute heat release rate (HRR), forward and reverse reaction rates of reactions, and transient temperature during the thermal ignition stage are decreased, as are misfires. When the intake air pressure is increased, the rates of important reactions also increase rapidly. The auto-ignition points are advanced by a crank angle degree (CAD) of 6°. In the combined ca
The mechanism of the partial oxidation of methane has been investigated over a bimetallic Pt-Ru catalyst. Dedicated experiments aimed to separate and quantify the relative contribution of single reactions included in the so-called "combustion and reforming" mechanism using the same catalyst. The catalyst is 0.5% Ru and 0.5% Pt (w/w) supported on mixture of alumina, ceria and zirconia (75/4.4/20.6%, w/w), washcoated on a ceramic monolith. Steam reforming, dry reforming, direct and reverse water-gas shift reactions were investigated. The temperature range investigated is 300 < T < 800 degrees C, while the space velocity range is 25.000 < GHSV < 100.000 h(-1). Conditions at which single side reactions are expected to occur during the partial oxidation process, were approximated by tuning the reactant composition. The experimental results are also compared with thermodynamic equilibrium calculations. The CO and H-2 yields of partial oxidation have been quantitatively connected with steam and dry reforming, while the persistent water-gas shift reaction always rearranges the products and intermediates.
for combustion processes, reactions are not complete due to the presence of reverse reactions which … society also demands that all the resulting combustion processes be clean, safe and efficient. Combustion … It also helps readers to understand how combustion processes can be more efficiently controlled and utilised
This report details the design of a test stand that converts carbon dioxide and hydrogen into methanol via a two-step process. The first step is a reverse water-gas shift reaction, carried out at 600°C and 25 bar to reduce carbon dioxide to carbon monoxide, and the second is a synthesis reaction that forms methanol at 260°C and 75 bar. The purpose of the system is to test catalysts for each of these steps. The test stand produces approximately 1.5 gallons of crude methanol (methanol mixed with water) per day, and recycles unreacted syngas for increased efficiency. At peak recycle, the stand is expected to consume 0.29 cylinders per day of carbon dioxide and 1.43 cylinders per day of hydrogen. It is planned to be built next to the Blue Star electrolysis unit in the Energy Systems Laboratory (ESL) and includes future plans of acquiring hydrogen from that stand rather than gas cylinders. At this phase of research, three key documents have been produced, as summarized in Table 1. These documents are primarily intended to describe the system and its operation, demonstrate that selected components are appropriate for the intended application, identify potential hazards, safeguards, and mitigation strategies, and ensure that the system is designed to appropriate standards. The body of the report and its appendices provide a narrative of the work completed in FY25. The parts required to build the test stand will be procured and assembled in FY26. Testing will be conducted in the fina
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