Performance and emissions characteristics of a lean-burn marine natural gas engine with the addition of hydrogen-rich reformate

The exhaust gas-fuel reforming technique known as reformed exhaust gas recirculation (REGR) can generate on-board hydrogen-rich gas mixture (i.e., reformate) by catalytic reforming of the exhaust gas and fuel added into the reformer and then recirculate the reformate into the engine cylinder, which can realize the combination of hydrogen-rich lean combustion and exhaust gas recirculation. The REGR technique can be employed to achieve efficient and stable lean-burn combustion for the marine engine fueled with natural gas (i.e., marine NG engine) and it is considered as an effective way to meet the stringent ship emissions regulations. In the present study, an experimental investigation into the effects of reformate addition ratio (R_re) and excess air ratio (λ) on the combustion and emissions characteristics of a marine NG engine under various loads was conducted, and the potential of applying the REGR technique in a marine NG engine to achieve low emissions (i.e., International Maritime Organization Tier Ⅲ emissions legislations for international ships) was discussed. The results indicate that the addition of the hydrogen-rich reformate gases can extend lean-burn limit. For a given λ, the flame development duration and rapid combustion duration decrease with the increase of R_re, and the combustion efficiency is improved. The brake specific NO_x emissions first increase and then decrease with the increase of R_re due to the competition between the combustion phase and total heat release value. The brake specific THC emissions decline with the increase of R_re, while the reverse holds for the brake specific CO emissions, and the behavior tends to be obvious under large λ. It is demonstrated that the combination of REGR and the lean-burn combustion strategy can improve the trade-off relationship between the NO_x emissions and brake specific fuel consumption of the marine NG engine to meet the IMO Tier Ⅲ NO_x emissions legislations and maintain relatively low brake specific fuel consumption.     

Effects of reformed exhaust gas recirculation on the HC and CO emissions of a spark-ignition engine fueled with LNG

Reformed exhaust gas recirculation (REGR), which can generate onboard hydrogen-rich gas (i.e., the reformate including H₂, CO, unreformed hydrocarbon, etc.) via catalytic reforming of fuel and engine exhaust gas, is an attractive way to improve the performance and emissions characteristics of the engine fueled with liquefied natural gas (i.e., NG engine). However, the leakage during the valve overlap period and incomplete burning of the added reformate may lead to extra HC and CO emissions from the engine with REGR. In the present study, a multi-dimensional computation fluid dynamics model coupled with a detailed chemical kinetic mechanism was developed to investigate the effects of the ratio of reformate addition (R_ref) and exhaust valve closed (EVC) timing on the total emissions characteristics as well as the sources of HC and CO emissions from the engine. The emissions from the combustion and the leaking were included to calculate the total emissions. Moreover, the unburned CO from the added reformate was distinguished from the total CO emissions by adding marked-species. Results show that the unburned CH₄ in the cylinder is the main component of the total CH₄ emissions. Due to the increase of the concentrations of OH, O and H radicals during the combustion process, the oxidization of CH₄ is promoted with the increase of R_ref at high load, and therefore the total CH₄ emissions decrease. However, the total CO emissions increase with the increase of R_ref, and it is demonstrated that the unburned CO from the added reformate increases and turns to be the main sources of the total CO emissions. At R_ref of 10%, the total CH₄ and CO emissions firstly remain nearly constant and then increase dramatically with the delay of EVC timing. Therefore, low concentration of CO in the reformate and short valve duration are recommended to achieve low HC and CO emissions for the NG engine with REGR.     

Improving gasoline direct injection (GDI) engine efficiency and emissions with hydrogen from exhaust gas fuel reforming

Exhaust gas fuel reforming has been identified as a thermochemical energy recovery technology with potential to improve gasoline engine efficiency, and thereby reduce CO₂ in addition to other gaseous and particulate matter (PM) emissions. The principle relies on achieving energy recovery from the hot exhaust stream by endothermic catalytic reforming of gasoline and a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the gasoline fed to the reformer and is recirculated to the intake manifold, i.e. reformed exhaust gas recirculation (REGR).     

On-board generation of hydrogen to improve in-cylinder combustion and after-treatment efficiency and emissions performance of a hybrid hydrogen–gasoline engine

Hydrogen on-board fuel reforming has been identified as a waste energy recovery technology with potential to improve Internal combustion engines (ICE) efficiency. Additionally, can help to reduce CO₂, NO_x and particulate matter (PM) emissions. As this thermochemical energy is recovered from the hot exhaust stream and used in an efficient way by endothermic catalytic reforming of petrol mixed with a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the petrol fed to the reformer and is recirculated to the intake manifold, which will be called reformed exhaust gas recirculation (rEGR).The rEGR system has been simulated by supplying hydrogen (H₂) and carbon monoxide (CO) into a conventional Exhaust Gas Recirculation (EGR) system. The hydrogen and CO concentrations in the rEGR stream were selected to be achievable in practice at typical gasoline exhaust temperatures (temperatures between 300 and 600 °C). A special attention has been paid on comparing rEGR to the baseline ICE, and to conventional EGR. The results demonstrate the potential of rEGR to simultaneously increase thermal efficiency, reduce gaseous emissions and decrease PM formation.Complete fuel reformation can increase the calorific value of the fuel by 28%. This energy can be provided by the waste heat in the exhaust and so it is ideal for combination with a gasoline engine with its high engine-out exhaust temperatures.The aim of this work is to demonstrate that exhaust gas fuel reforming on an engine is possible and is commercially viable. Also, this paper demonstrates how the combustion of reformate in a direct injection gasoline engine via reformed Exhaust Gas Recirculation (rEGR) can be beneficial to engine performance and emissions.     

Catalytic exhaust gas fuel reforming for diesel engines—effects of water addition on hydrogen production and fuel conversion efficiency

Previous work in our laboratory has shown that the exhaust gas assisted fuel reforming process has the potential to provide a solution to the diesel engine exhaust emission problems. When simulated reformer product gas rich in hydrogen is fed to the engine, a reduction of both NO_x and smoke emissions can be achieved. In this paper, the optimisation of the reforming process by water addition in the reactor is presented. Using a prototype catalyst at 290°C reactor inlet temperature, up to 15% more hydrogen in the reformer product was obtained compared to operation without water. The process has been found to be mainly a combination of the fuel oxidation, steam reforming and water gas shift reactions. The reforming process efficiency has been shown to improve considerably with water addition up to a certain level after which the adverse effects of the exothermic water gas shift reaction become significant.     

Experimental study on partial oxidation of methane to produce hydrogen using low‐temperature plasma in AC Glidarc discharge

A reformer using low‐temperature plasma was designed and developed for hydrogen production. The reformer has three electrodes and uses AC gliding arc discharge. A reference condition, which is the highest hydrogen production, has a O₂/C ratio of 0.45, input flow rate of 4.9 l min^?1 and power supply of 1 kW. And the methane conversion rate, the high hydrogen selectivity and the reformer efficiency were 69.2, 77.8 and 35.2%, respectively. To investigate reforming characteristics, parametric studies were achieved for the gas components ratio, a gas flow rate, a reactor temperature, an input electric power and catalyst addition effect. The results are as follows: The gas components ratio was an important factor, which had maximum value. When the gas flow rate, the reactor temperature and the electric power were increased, the methane conversion rate and the hydrogen concentration also increased. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance analysis of a membrane‐based reformer‐combustor reactor for hydrogen generation

Hydrogen is mostly produced in conventional steam methane reforming plants. In this work, we proposed a membrane‐based reformer‐combustor reactor (MRCR) for hydrogen generation in order to improve heat recovery and overall thermal efficiency. The proposed configuration will also reduce the complexity in existing steam methane reforming (SMR) plants. The proposed MRCR comprises combustion zone, hydrogen permeate zone, and SMR zone. A computational fluid dynamics model was developed using ANSYS‐Fluent software to simulate and analyze the performance of the proposed MRCR. Results show that high hydrogen yields were observed at high reformer pressures (RPs) and low gas hourly space velocities (GHSVs). Furthermore, by increasing the steam to methane ratio and addition of excess air in the combustion side, the hydrogen yield from the MRCR decreases. This is attributed to the reduction in the effective temperature of the hydrogen membrane. High RP, low GHSV, and low steam to methane ratio that increased the hydrogen yield also decreased carbon monoxide (CO) emissions. For an increased RP from 1 to 10 bar, the CO emission decreased by about 99%. The reduction in CO emission at high RP would be attributed to the effect of water gas shift reaction in the MRCR. Results of the extensive parametric study presented in this work can be used to determine the operating conditions based on tradeoffs between hydrogen yield (mole H₂/mole CH₄), hydrogen production rate (kg of H₂/h), allowable CO emissions, and exhaust gas temperature for other applications such as gas turbine.     

Ammonia as hydrogen carrier for transportation; investigation of the ammonia exhaust gas fuel reforming

In this paper we show, for the first time, the feasibility of ammonia exhaust gas reforming as a strategy for hydrogen production used in transportation. The application of the reforming process and the impact of the product on diesel combustion and emissions were evaluated. The research was started with an initial study of ammonia autothermal reforming (NH₃ – ATR) that combined selective oxidation of ammonia (into nitrogen and water) and ammonia thermal decomposition over a ruthenium catalyst using air as the oxygen source. The air was later replaced by real diesel engine exhaust gas to provide the oxygen needed for the exothermic reactions to raise the temperature and promote the NH₃ decomposition. The main parameters varied in the reforming experiments are O₂/NH₃ ratios, NH₃ concentration in feed gas and gas – hourly – space – velocity (GHSV). The O₂/NH₃ ratio and NH₃ concentration were the key factors that dominated both the hydrogen production and the reforming process efficiencies: by applying an O₂/NH₃ ratio ranged from 0.04 to 0.175, 2.5–3.2 l/min of gaseous H₂ production was achieved using a fixed NH₃ feed flow of 3 l/min. The reforming reactor products at different concentrations (H₂ and unconverted NH₃) were then added into a diesel engine intake. The addition of considerably small amount of carbon – free reformate, i.e. represented by 5% of primary diesel replacement, reduced quite effectively the engine carbon emissions including CO₂, CO and total hydrocarbons.     

Simulation of steam reforming of biogas in an industrial reformer for hydrogen production

The paper aims to investigate the steam reforming of biogas in an industrial-scale reformer for hydrogen production. A non-isothermal one dimensional reactor model has been constituted by using mass, momentum and energy balances. The model equations have been solved using MATLAB software. The developed model has been validated with the available modeling studies on industrial steam reforming of methane as well as with the those on lab-scale steam reforming of biogas. It demonstrates excellent agreement with them. Effect of change in biogas compositions on the performance of industrial steam reformer has been investigated in terms of methane conversion, yields of hydrogen and carbon monoxide, product gas compositions, reactor temperature and total pressure. For this, compositions of biogas (CH₄/CO₂ = 40/60 to 80/20), S/C ratio, reformer feed temperature and heat flux have been varied. Preferable feed conditions to the reformer are total molar feed rate of 21 kmol/h, steam to methane ratio of 4.0, temperature of 973 K and pressure of 25 bar. Under these conditions, industrial reformer fed with biogas, provides methane conversion (93.08–85.65%) and hydrogen yield (1.02–2.28), that are close to thermodynamic equilibrium condition.     

Modelling and experimental investigation of compact packed bed design of methanol steam reformer

A comprehensive mathematical model was developed to analyse methanol steam reforming in catalytic packed-bed tubular reactor. All the important aspects of reaction kinetics of main reactions and thermodynamic terms of heat and mass transfer were studied for commercially available CuO/ZnO/Al₂O₃ catalysts from Süd-Chemie. This numerical model was simulated using Engineering Equation Solver (EES). Through the set of organized simulation studies, the basic operational boundary conditions of operating temperature (573 K) with respect to complete conversion of methanol and optimum hydrogen generation, optimum S/C ratio (1.4) of methanol water mixture feed and operating capacity of one tubular reactor array were discovered. At temperatures near 573 K it was found that the reformate gas does not require any purification/filtration to be supplied to a HT-PEMFC as the CO concentration in reformate gas was low (below 30000 ppm). The simulation work for understanding the effect of different operating condition(s) on the reformer performance generated design of experiment for investigation of the efforts carried out to evaluate, build and demonstrate a 0.25 kWe equivalent methanol reformer for HT-PEM fuel cell system.The paper discusses few of the important aspects on the experimental investigation of effect of operating conditions on methanol steam reformer design with packed bed configuration for hydrogen production. The basic investigation included the analysis of effect of design and operating parameters on the methanol conversion and quality of reformate gas generation (amount of CO). The investigation also covers the analysis of heat and mass transfer along with chemical reaction and generation of species to achieve optimum process parameters and system efficiency. These investigations led to finalise, the operating parameters and basic design philosophy of the packed bed tubular methanol steam reformer for 5 kWe HT-PEMFC system application.     

Biogas upgrading for on-board hydrogen production: Reforming process CFD modelling

Hydrogen production through fuel reforming can be used to improve IC (internal combustion) engines combustion characteristics and to lower vehicle emissions. In this study, a computational fluid dynamics (CFD) model based on a detailed kinetic mechanism was developed for exhaust gas reforming of biogas to synthetic gas (H₂ and CO). In agreement with experimental data, the reactor's physical and chemical performance was investigated at various O₂/CH₄ ratios and gas hourly space velocities (GHSV). The numerical results imply that methane reforming reactions are strongly sensitive to O₂/CH₄ ratio and engine exhaust gas temperature. It was also found that increasing GHSV results in lower hydrogen yield; since dry and steam reforming reactions are relatively slow and are both dependent on the flow residence time. Furthermore, the hot spot effect, which is associated to oxidation reforming reactions, was investigated for catalyst activity and durability.     

Optimization of bio-ethanol autothermal reforming and carbon monoxide removal processes

Experimental investigation of bio-ethanol autothermal reforming (ATR) and water-gas shift (WGS) processes for hydrogen production and regression analysis of the data is performed in the study. The main goal was to obtain regression relations between the most critical dependent variables such as hydrogen, carbon monoxide and methane content in the reformate gas and independent factors such as air-to-fuel ratio (λ), steam-to-carbon ratio (S/C), inlet temperature of reactants into reforming process (T_ATRin), pressure (p) and temperature (T_ATR) in the ATR reactor from the experimental data. Purpose of the regression models is to provide optimum values of the process factors that give the maximum amount of hydrogen. The experimental ATR system consisted of an evaporator, an ATR reactor and a one-stage WGS reactor. Empirical relations between hydrogen, carbon monoxide, methane content and the controlling parameters downstream of the ATR reactor are shown in the work. The optimization results show that within the considered range of the process factors the maximum hydrogen concentration of 42 dry vol. % and yield of 3.8 mol mol⁻¹ of ethanol downstream of the ATR reactor can be achieved at S/C = 2.5, λ = 0.20-0.23, p = 0.4 bar, T_ATRin = 230 °C, T_ATR = 640 °C.     

The effect of reformer gas mixture on the performance and emissions of an HSDI diesel engine

Exhaust gas assisted fuel reforming is an attractive on-board hydrogen production method, which can open new frontiers in diesel engines. Apart from hydrogen, and depending on the reactions promoted, the reformate typically contains a significant amount of carbon monoxide, which is produced as a by-product. Moreover, admission of reformed gas into the engine, through the inlet pipe, leads to an increase of intake air nitrogen to oxygen ratio. It is therefore necessary to study how a mixture of syngas and nitrogen affects the performance and emissions of a diesel engine, in order to gain a better understanding of the effects of supplying fuel reformer products into the engine.     

Study on hydrogen-rich syngas production by dry autothermal reforming from biomass derived gas

In this study, the H₂-rich syngas (H₂ + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO₂/CH₄ and O₂/CH₄ molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO₂ concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H₂/CO molar ratio between 1 and 2 was achieved by varying CO₂/CH₄ molar ratio. However, the syngas concentrations were affected by CO₂/CH₄ and O₂/CH₄ molar ratio.     

Research and development of a low-BTU gas-driven engine for waste gasification and power generation

Combustion characteristics of low-BTU gases (about 1000 kcal/N m³) were experimentally investigated in order to develop engine generators for waste gasification and power generation systems. Two simulated low-BTU gases, obtained from one-step high temperature gasification (hydrogen rich) and two-step pyrolysis/reforming gasification (methane rich), as well as natural gas, were tested in a small-scale spark ignition engine. Compared to the natural gas driven engine, the hydrogen rich low-BTU gas driven engine showed similar thermal efficiency but with significantly lower NO_x and hydrocarbon emissions and wider equivalence ratio range for stable engine operation. On the other hand, the methane rich low-BTU gas engine showed narrower equivalence ratio range for stable operation. The test results show engine performance more depends on combustion characteristics than on the heating value of the fuel gas. For better engine performance, hydrogen rich fuel gas is desirable.     

Hydrogen production from bioethanol fuel mixtures via exhaust heat recovery in diesel engines: A promising route towards more energy efficient road vehicles

Bioethanol has been considered a potential alternative to the conventional fossil fuels in transportation sector as well as a hydrogen carrier. This study proposes a thermochemical recovery pathway to extend the use of bioethanol in compression ignition engines through catalytic exhaust gas reforming of ethanol-biodiesel-diesel blends into hydrogen. The aim is to improve the heat recovery of the engine exhaust gas and increase the on-board production of hydrogen which can potentially partially replace the diesel fuel in the engine. Results indicate that the effectiveness of the reforming process mainly depends on the blend composition, reforming temperature, and oxygen to carbon ratio (O/C). It is deduced that ethanol content in the fuel blend has a key role in sustaining catalyst activity and hydrogen production. Overall, the study highlights the positive impact and practicality of recovering exhaust heat using the ethanol-biodiesel-diesel blends. This implementation can result in noticeable improvements in emission reduction of diesel powertrains once the reformate is fed back into the engine.     

Hydrogen in plasma-assisted hydrocarbon selective catalytic reduction

Onboard plasma reforming has strong potential for use in supplying reductants for hydrocarbon selective catalytic reduction (HC SCR) of NO_x in vehicle exhaust. However, the role of hydrogen as an additional reductant with various catalysts at various temperatures remains unclear. Here we investigated the de-NO_x performance of HC SCR with Pt-based and Ag/Al₂O₃ catalysts at various temperatures using hydrogen and hydrocarbons supplied directly or generated onboard by plasma reforming using engine bench-level tests. Further, we clarified the specific role of hydrogen in the process. We found that with Pt-based catalysts, hydrogen is oxidized to H₂O or promotes full oxidation of hydrocarbon, thus having no positive effect. By contrast, with Ag/Al₂O₃, hydrogen only promotes partial oxidation of hydrocarbon to yield surface intermediates that significantly facilitate SCR. Furthermore, reductants generated by plasma reforming exhibit better de-NO_x performance than directly supplied gas mixtures. Thus, onboard plasma onboard reforming can be an important strategy for effective HC SCR.     

Enhancing the NO2/NOx ratio in compression ignition engines by hydrogen and reformate combustion,for improved aftertreatment performance

Enhanced NO₂ production (without raising total NOx) in a diesel engine combustion chamber can improve the performance of several catalytic aftertreatment systems. Thus this can facilitate a further reduction in key regulated emissions such as nitrogen oxides (NOx) and particulate matter (PM) emissions. The oxidation of NO to NO₂ is an important intermediate step involved in all current aftertreatment systems that are designed for NOx and PM catalytic removal. The performance of both NOx control systems and catalysed particulate filters depend highly on the NO₂ concentration. In this work we have examined the influence of using hydrogen (H₂) and simulated reformate (H₂, CO and EGR gases) as a supplement to diesel fuel on NO₂ production. In actual engine applications a reformer will be integrated within the engine EGR system. This will not only provide the engine with recirculated exhaust gas (i.e. EGR), but will enrich it with H₂ and CO.     

A hybrid fuel cell system integrated with methanol steam reformer and methanation reactor

In this paper, a hybrid fuel cell system integrated with methanol steam reformer and methanation reactor is demonstrated. Methanol steam reformer employed in this system is to produce hydrogen-rich reformate in connection with a methanation reactor to reduce the carbon monoxide content effectively, and the reformate gas is sent into a low-temperature polymer electrolyte fuel cell for direct electric power generation. The optimum conditions (temperature, water to methanol ratio, and space velocity) for methanol steam reforming (MSR) reaction and methanation (MET) reaction are verified by experiments. A comparison between pure hydrogen, reformate surrogate, and actual reformate is performed. The results show that the power density of this hybrid system achieves 245.2 mW/cm² while it achieves 268.8 mW/cm² when employing pure hydrogen as the fuel. An alternative novel method to solve the problem of hydrogen storage and transportation is provided and the in-situ hydrogen production and utilizing through low-temperature fuel cell system is realized, which is helpful to accelerate the commercialization process of the fuel cell.     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.