Natural Gas Fueled Engine Research Articles

Exhaust purification of stoichiometric natural gas applications – A screening study on the impact of catalyst composition, reaction conditions and transient effects

A set of model catalysts with a variation of precious metal components comprising Pt, Pd or Pt/Pd on typical support materials (CeO2, Al2O3 and ZrO2) is evaluated in a gas mixture simulating the exhaust gas of stoichiometric natural gas-fueled engines. Three-way catalytic (TWC) performance, especially CH4 conversion, is assessed in λ-sweep as well as dynamic light-Off/light-Out tests, both with oscillating feed (1 s lean /1 s rich) implemented on a fully automated reactor system. The transient response of catalysts to changing redox potential is demonstrated in tests with varying lean/rich duration and pseudo-stationary tests. Time resolved data clearly indicate that performance and stability depend on both, precious metal composition as well as support material. Beyond screening of catalyst activity, the focus was on factors affecting the formation of undesired by-products (e.g. NH3, N2O) on hydrothermally aged catalysts. Aging severity was introduced as additional dimension in the design of the experimental study.

Compact, real-time exhaust gas recirculation rate sensor for use in natural gas combustion engine control

Natural gas fueled engines offer a 25% reduction in greenhouse gas emissions compared to diesel. However, achieving similar fuel efficiency to diesel while also minimizing harmful emissions is a challenge. Emissions and efficiency targets can be simultaneously achieved for natural gas by using a three way catalyst and exhaust gas recirculation (EGR), but this requires that the air-fuel ratio and EGR rate be measured and precisely controlled to avoid knocking combustion while maximizing efficiency. Such on-engine control can be achieved with high speed, precise, and robust measurements of EGR rate at a size and cost level compatible with onboard control systems. In this work, we present a compact, real-time laser absorption spectroscopy-based EGR sensor with potential for low-cost, on-engine control. We develop a new, computationally efficient data fitting algorithm called Integral Hashing to enable fully autonomous, low latency, real-time operation of the laser sensor at 954Hz. The complete sensor, including lasers and drivers, data acquisition, and data processing is contained in a single 25 × 25 × 8cm enclosure supplied with 15W of power. We validate the sensor to within 2% EGR rate against an extractive non-dispersive infrared (NDIR) gas sensor on a 250kW 6 cylinder natural gas engine by simultaneously measuring a set of steady state EGR rates between 0% and 25%. Additionally, we measure transient EGR rate fluctuations that are too fast to detect with the NDIR measurement. The sensor system presented here could be used to precisely control the EGR rate, improving the efficiency, emissions, and overall adoption of natural gas engines.

Investigation on novel natural gas fueled homogeneous charge compression ignition engine based combined power and cooling system

A significant part of energy of fuel supplied is lost in internal combustion engines in the form of atmospheric discharge of engine exhaust gases which are considered as a big source of engine inefficiency and formation of pollutant emissions. To address this issue, a bottoming cycle combining the transcritical CO2 (T-CO2) refrigeration cycle and the supercritical CO2 (sCO2) power cycle is employed, aiming to produce cooling for food preservation by utilizing the exhaust heat of homogeneous charge compression ignition (HCCI) engine powering the refrigerated truck. The operative variables and their effect on thermal and exergetic efficiency of HCCI engine and the combined system are investigated. At the base case operative conditions, the thermal and exergy efficiencies of natural gas fueled HCCI engine are improved significantly from 48.69% to 61.28% and from 41.14% to 42.79%, respectively, after employing the sCO2 powered T-CO2 refrigeration cycle. Promotion of equivalence ratio from 0.3 to 0.9 enhances the thermal and exergy efficiencies of HCCI engine from 47.44% to 49.54% and from 40.14% to 42.12%, respectively. Increasing of engine speed from 1400 r.p.m to 2200 r.p.m provides marginal improvement in HCCI engine efficiencies but the efficiencies of combined cycle are significantly improved from 57.67% to 65.18% and from 40.64% to 45.06%, respectively. Finally, exergy analysis applied to determine the sources of non-idealities within the system revealed that out 361 kW (100%) fuel exergy supplied to the system, HCCI engine destroys 93.31 kW (25.85%), catalytic convertor destroys15.49 kW (4.29%), and the in-cylinder heat transfer losses and system exhaust losses are found as 35.72 kW (9.91%) and 16.61 kW (4.61%), respectively.

Computational analysis of performances for a hydrogen enriched compressed natural gas engine’ by advanced machine learning algorithms

The support vector machine along with particle swarm optimization and artificial neural network have already been implemented for the regression study of a hydrogen enriched compressed natural gas (HCNG) fueled spark ignition engine. The main issues were that the support vector machine along with particle swarm optimization requires more computational time while the artificial neural network is sensitive to the hidden layers. Therefore, these algorithms are not effectively suitable for online control of the electronic control unit. The theme of this study is to evaluate the multiple mathematical engine’ models with respect to swiftness and accuracy. The experiments have been conducted under a wide range of operating conditions in a heavy-duty SI engine to obtain the data sets. The brake specific fuel consumption, engine torque and NOx emissions have been trained and analyzed by eight different machine learning algorithms along with nineteen sub-models. The effectiveness of these algorithms has been evaluated with respect to the root mean squared error and prediction time. The analysis indicate that the gaussian process regression (GPR) is optimal with respect to the computational efficiency (i.e., RMSE = 0.3823 g/kWh) and time (t < 16.019 sec). Furthermore, it operates without the iteration of the hidden layers. The mean simulation time for the gaussian process regression is 20,192 times lower as compared to the support vector machine along with particle swarm optimization algorithm. Since the gaussian process regression (GPR) is fast, optimal and insensitive to the hidden layers, so it is an ideal tool for online calibration of the electronic control unit.

Numerical study on a natural gas-fueled engine under low temperature combustion mode

Natural gas, which is also referred to as eco-friendly fuel, is being seen as a potential solution to challenge the decline of crude oil resources and the deteriorating air quality in urban areas. This fuel has been verified to emit less CO, HC, and PM compared to other fuels. A potential approach to reducing NOx and soot emissions while also achieving low fuel consumption is the low temperature combustion process. In this study, internal combustion engines were simulated under various conditions. The objective was to investigate the effect of different operating variables on the low temperature combustion mode. To begin with, a natural gas powered engine was modeled using complex chemical kinetics software. The outcomes of the simulation were then compared to experimental data, demonstrating a high level of agreement. Subsequently, the impacts of key variables, including the air-fuel ratio, compression ratio, and engine speed, were analyzed using a cycle simulation code. Increasing the compression ratio improves engine performance, and the specific fuel consumption decreases. However, it leads to a significant increase in NOx emissions until a certain value. Thereafter, it changes the trend. Engine speed indirectly affects performance by increasing fuel consumption and changing ignition timing. A leaner air fuel ration may be used to produce more power and keep the temperature of combustion below a certain value (low-temperature combustion), ensuring low NOx emissions.

Robust model-based switching MIMO air handling control of turbocharged lean-burn SI natural gas variable speed engines

This paper demonstrates a multiple-input multiple-output (MIMO) controller design framework and a controller switching algorithm for MIMO controllers in their state-space form, which together achieve robust, efficient control of turbocharged lean-burn engines over a wide operating space. The controller design framework requires a linearized plant model, and uses the [Formula: see text]-synthesis and DK-iteration algorithms while considering state and output uncertainties and actuator bandwidths to synthesize a robust [Formula: see text] controller. A controller switching methodology using slow-fast controller decomposition and also incorporating hysteresis at switching points is utilized to smoothly transfer control authority between several MIMO controllers. The approach is applied to a high-fidelity truth-reference GT-Power engine model for a lean-burn natural gas-fueled engine to evaluate the closed-loop controller performance. The multi-tracking control problem targets engine speed, differential pressure across throttle as well as air-to-fuel ratio to achieve satisfactory engine performance and emissions without compressor surge. The engine response obtained using the robust MIMO controller is compared with that obtained using a state-of-the-art benchmark controller to evaluate the additional benefits of the MIMO controller.

Experimental approach for reducing nitrogen oxides emissions from ammonia–natural gas dual-fuel spark-ignition engine

In this study, characteristics of nitrogen oxides (NOx) emissions from an ammonia–natural gas dual-fuel operation were investigated by conducting spark-ignition engine experiments under the maximum load and a low engine speed (∼1,100 rpm). The feasibility of using a conventional selective catalytic reduction (SCR) system to reduce the NOx emissions was also investigated. For the experiments, an 11-L six-cylinder spark-ignition engine was used with appropriate modifications to use natural gas and ammonia together as the fuel. Several species comprising NOx emissions (NO, NO2, and N2O) and ammonia were measured together using a Fourier transform infrared analyzer (FT-IR). An aftertreatment system, including an SCR system and an ammonia oxidation catalyst (AOC), for an original natural gas-fueled engine was used to reduce engine-out NOx using the unburned ammonia as a reducing agent.From the experimental results, it was found that the NO concentration first increased on the addition of ammonia, as the fuel NOx emissions were produced. However, the total NO concentration became saturated with increasing ammonia fraction, owing to the increased amount of unburned ammonia. Specifically, considering the trend of the burned gas temperature and its value at exhaust valve opening (EVO) timing, it is inferred that nitrogen oxide was reduced owing to unburned ammonia after the exhaust valve opening timing, where the temperature range of combustion product was suitable to trigger selective non-catalytic reduction (SNCR). The remaining ammonia, after the SNCR, was then virtually oxidized to reduce the remaining NO while passing SCR system, showing an almost zero level (<10 ppm) at the catalyst-out level. N2O and NO2 were produced in the order of tens and hundreds of ppm, respectively. Thus, despite the high level of global warming potential (GWP) of N2O, its contribution to global warming effect was not significant. On the other hand, the unburned methane was particularly increased at some point with poor combustion efficiency to offset the effect of decrement in carbon dioxide due to its high level of GWP.

Heterogeneous chemical reactions—A cornerstone in emission reduction of local pollutants and greenhouse gases

The current state and challenges of advanced experimental and modeling methods for a better understanding of heterogeneous chemical reactions are discussed using examples from developing and future technologies in the area of emission reduction of local pollutants and greenhouse gases. In situ and operando experimental techniques using laser and X-ray absorption spectroscopy, for instance, are able to resolve spatial and temporal concentration and temperature profiles in the near-wall gas phase, the interphase and inside the solid bulk. They have been exploited for a better understanding of the interaction of chemical reactions and transport processes. The experimental elucidation of chemical conversion on the microscopic scale leads to elementary step-like surface reaction mechanisms. The microkinetic description of gas-surface reactions is still challenging due to the complex influence of the modification of the solid material itself on the microscopic scale during the chemical reaction, which is caused by intrinsic materials’ modifications due to adsorbed species and temperature variations. Furthermore, transient inlet and boundary conditions on the reactor scale have a strong impact on the material and reaction rate. In addition to thermochemical reactions, an additional complexity comes into play with electrochemical ones. This paper will discuss heterogeneous chemical reactions in the light of emerging technologies such as emission control of natural gas and hydrogen fueled engines, use of CO2 in chemical (methanation, dry reforming) and steel industry (off-gas reforming), hydrogen production by pyrolysis of methane, small-scale ammonia synthesis and use, and recyclable carbon-free energy carriers. Hence, this article will also reveal a new playground and the potential of methods, know-how, and skills of the combustion community to significantly contribute to the solution of climate-change relevant challenges.

About the possibility of using natural gas as a fuel on agricultural tractors

AIMS: Evaluation of the effectiveness of converting diesel engines used in agricultural self-propelled vehicles to fully or partially natural gas (methane) fueled engines.&#x0D; METHOD: Is analytical.&#x0D; RESULTS: In agriculture up to 25% of operating expenses are fuel costs. However, the only number of the concomitant objective and subjective factors allow us to estimate expedience and efficiency of converting diesel engines used in agricultural self-propelled vehicles for full or partial supply of natural gas (methane). On the one hand, the price of an equivalent amount (in terms of work performance) of natural gas is more than 2 times lower than the price of diesel fuel. At the same time, natural gas is the most environmentally friendly hydrocar-bon fuel. But, on the other hand, the underdeveloped refueling infrastructure is obvious, and the environmental friendliness of natural gas itself is not a guarantee of the environmental friendliness of the engine itself. Also, the safety of gas equipment operation under high pressure is an important matter.&#x0D; CONCLUSIONS: Firstly, the use of natural gas instead of diesel fuel requires taking into account the difference in the physicochemical characteristics of these fuels, which determines both the requirements for the organization of the working process and the advantages and disadvantages of such replacement. Secondly, the combustion process of natural gas, compared to diesel fuel, is characterized by in-creased formation of water leading to more intensive watering of lubricating oil, although it re-duces carbon dioxide emission into the atmosphere. Safety of natural gas equipment operation plays an important role, and first of all, it is concern of cylinders that are filled at pressure of 20.025.0 MPa.

Approaches for emission reduction in natural gas fueled direct-injection engines

A glow plug (GP) can serve as an effective ignition source in a heavy-duty direct-injection natural gas (DING) engine. Ignition performance can be improved by shielding the GP. The shield protects the GP from cooling by the injected natural gas (NG) jets and also traps NG next to the GP surface, acting as kind of pre-combustion chamber. Achieving rapid filing of the shield by a fuel jet and facilitating flame propagation out are key goals of shield design. However, previous studies found that emissions such as unburned CH4 and soot particles could be trapped inside the shield especially near its top end, contributing a large fraction to the engine exhaust. In this paper, new designs either controlling the NG amount entering the shield or improving the emission propagation out of the shield are proposed to solve the emission issues, and the impacts of these design changes on fuel injection and combustion emissions were computationally investigated. The base case includes an injector with nine 0.2 mm diameter nozzles and a diamond-pattern multi-opening GP shield. A new injector combining one smaller nozzle directed towards the GP shield and eight regular size nozzles was compared, while a new five-opening shield design adding a small opening on the top end of the diamond-pattern shield was studied. Compared to the base case, the new two-nozzle-size injector greatly reduced the amount of fuel injected into the shield, which solved the emission issues inside the shield. Over 35% and 95% reductions in the total mass of unburned CH4 and soot particles respectively were achieved. Furthermore, the additional opening for the new shield provides an alternative route for fuel flowing out of the shield during fuel injection. However, fuel injection is the main force for fuel motion inside the shield and highly affects the new flow route provided by the additional opening. The unburned CH4 and formed soot particles could not flow out of the shield through the additional opening once fuel injection is finished. Generally, an increase was found for the unburned CH4 and soot mass by using the new five-opening shield, compared to the base case.

Development of a High-Performance Solenoid Gas Injector Applied for Compressed Natural Gas Fueled Engines

Development of a High-Performance Solenoid Gas Injector Applied for Compressed Natural Gas Fueled Engines

Performance, structure and kinetics of Pd catalyst supported in Ba modified γ-Al2O3 for low temperature wet methane oxidation

Low temperature wet methane oxidation is critical for the after-treatment of exhaust from the vehicles powered with natural gas-fueled engine, which is always operated at low temperatures and with high water vapor concentrations. Herein, Pd/Ba-Al2O3 catalysts were prepared, with different amount of Ba as the promoter. It was found that the Pd/Ba-Al2O3 catalysts were superior to the reference Ba-free Pd/Al2O3 catalyst in terms of methane conversion, intrinsic activity and hydrothermal stability. Based on the sufficient characterization results, the location, size, valence state and diverse properties of Pd regulated by Ba were revealed. The benefit from Ba addition on the catalytic performance was demonstrated to be derived from the favorable location of Pd inside the porous channel and the enhancement in the capability for O2 activation. This work can provide insights into the effect of promoters on the catalysts, offer an avenue to designing highly efficient wet methane oxidation catalyst, and lay a foundation for the application of Pd/Ba-Al2O3 in exhaust after-treatment for the natural gas-fueled vehicles.

Effects of Dilution and Flammability Changes on Mixture Reactivity in a Natural Gas Internal Combustion Engine

ABSTRACT Changes in the flammability characteristics of a combusting mixture and its ‘dilution’ levels – characterized, respectively, by the mixture’s equivalence ratio and residual gas fraction – can have significant impacts on the nature of combustion in internal combustion engines. These combustion changes can manifest as variations in combustion phasing and repeatability, and affect engine efficiency, emissions, and performance. The current work uses experimental, high-speed, in-cylinder CO2 concentration data from a single-cylinder, natural gas-fueled engine to track compositional variations in the combusting mixture; and then uses a chemical kinetics solver to isolate the effects of flammability and dilution changes on the mixture’s ‘reactivity,’ which is characterized by its laminar flame speed (LFS) and ignition delay (ID). It is found that LFS changes are driven strongly by the trapped equivalence ratio, while ID changes are driven primarily by dilution and pressure changes. Additionally, the effects of LFS changes on the overall combustion phasing are found to be more pronounced than those from ID changes, as the former influences both the combustion initiation and propagation processes.

Effects of working conditions on the operating characteristics of an injection system applied on CNG fueled vehicles

A model-based study is conducted to examine the operating characteristics of an injection system applied on CNG fueled vehicles. This injection system is a combination of an electric pressure regulator, a rail tube, and a solenoid injector. The electric pressure regulator has a great potential to be widely used in injection systems of natural gas-fueled engines due to its flexible operation, which can help to improve the engine performance and reduce emission. This paper presents a simulation study using mathematical models to describe and analyze the operating characteristics of the gaseous fuel injection system, in which models of electric pressure regulator, solenoid fuel injector, and control model for electric pressure regulator are presented. The simulation results are compared with experimental data to validate the simulation models. Effects of working conditions, including coil resistance of the electric pressure regulator, inlet gas pressure, and set pressure in the rail tube, on the operating characteristics of the gaseous fuel injection system are investigated. Simulation results show that when the coil resistance of the electric pressure regulator is increased from 3.1 Ω to 4.1 Ω, the maximum fluctuation of the controlled gas pressure in the rail tube is reduced from 0.017 to 0.012 MPa, respectively. By decreasing the inlet gas pressure of the electric pressure regulator from 2.5 to 2.3 MPa, the controlled gas pressure in the rail tube is more stable with the maximum fluctuation significantly reduced from 0.012 to 0.002 MPa, respectively, which leads to stability in injection flow rate. The increase of set pressure in the rail tube from 0.5 to 0.7 MPa can help to improve the stability of the controlled gas pressure in the rail tube with the maximum fluctuation respectively reduced from 0.002 to 0.001 MPa.

Cycle-skipping strategy with intake air cut off for natural gas fueled Si engine.

In this study, cycle-skipping was investigated for a natural gas engine which has single cylinder, unsupercharged with 1.16 L volume and spark ignition. Additionally, inlet manifold air was switched off during cycle-skipping to minimize pumping losses. Thus, cycle-skipping strategy was carried out, and its effects on emission and engine performance were investigated. Indicated mean effective pressure, indicated efficiency, specific emissions (CO, HC, and NOX) and combustion characteristics (in-cylinder pressure and rate of heat release) were investigated in the study. As a result of performed study, it is predicted that a significant improvement can be achieved in indicated thermal efficiency as 22.8% and 13.4% by different cycle-skipping strategies. However, there is not a continuous change in emissions for different cycle-skipping strategies. While CO and NOX emissions increased in 3N1S (three normal, one cycle-skip) condition, HC emissions decreased in accordance with normal condition. For both cycle-skipping strategies, all the emissions have an increase in accordance with normal condition. In 3N1S and 2N1S (two normal, one cycle-skip) cycle skip engine operating conditions, compared to engine operating under normal condition, CO emissions increased by 14.7 and 51.7 times, respectively. In terms of HC emissions, while emission values decreased by 27.8% under 3N1S operating conditions, they increased by 67.2% under 2N1S operating conditions. Finally, in 3N1S and 2N1S cycle skip engine operating conditions, NOx emissions increased by 3.7 and 6.9 times, respectively, compared to normal operating condition. Another significant result of this study is that peak in-cylinder pressure increased as the cycle-skipping rate increased.

High Ethylene and Propylene in an Area Dominated by Oil Production

We measured the spatial distribution and composition of ozone-forming hydrocarbons, alcohols, and carbonyls in Utah’s Uinta Basin during the winter months of 2019 and 2020. The Uinta Basin contains about 10,000 producing oil and gas wells. Snow cover and the region’s unique topography (i.e., a large basin entirely surrounded by mountains) promote strong, multi-day temperature inversion episodes that concentrate pollution and lead to wintertime ozone production. Indeed, organic compound concentrations were about eight times higher during inversion episodes than during snow-free springtime conditions. We examined spatial associations between wintertime concentrations of organics and oil and gas sources in the region, and we found that concentrations of highly reactive alkenes were higher in areas with dense oil production than in areas with dense gas production. Total alkene+acetylene concentrations were 267 (42, 1146; lower and upper 95% confidence limits) µg m−3 at locations with 340 or more producing oil wells within 10 km (i.e., 75th percentile) versus 12 (9, 23) µg m−3 at locations with 15 or fewer oil wells (i.e., 25th percentile). Twenty-eight percent of the potential for organic compounds to produce ozone was due to alkenes in areas with dense oil production. Spatial correlations and organic compound ratios indicated that the most likely source of excess alkenes in oil-producing areas was natural gas-fueled engines, especially lean-burning (i.e., high air:fuel ratio) artificial lift engines.

Choice of the Optimal Design and Operation of Multi-Energy Conversion Systems in a Prosecco Wine Cellar

Despite the high energy consumption of wine making processes, little efforts have been spent so far, both at the industrial and scientific level, to search for alternative energy systems in wine cellars. In fact, almost all the existing cellars take electricity from the grid and burn natural gas or other fossil fuels to fulfil their energy demands. This paper analyses the energy demands of a real Prosecco wine cellar in the North East of Italy, which can be considered as a “reference” cellar for dimensions and wine production. The goal is to find the best energy conversion system in terms of maximum profits, efficiency and share of renewable energy utilization. Four alternative design configurations are proposed, and each one optimized considering the three objectives. Results show that a 35% gain in the maximum profits is obtained by including a natural gas fueled CHP internal combustion engine and an absorption chiller. This configuration is also the best one to achieve the maximum efficiency (61%), resulting in 18% reduction of primary energy consumption. Conversely, the utilization of a biomass boiler and an absorption chiller allows maximizing the share of renewable energy consumption, which is about 35% considering the existing availability of biomass from pruning harvesting and the relative limited surface available for photovoltaic generation. This option may become economically interesting when the price of natural gas increases of at least 50%.

Numerical comparison of combustion characteristics and cost between hydrogen, oxygen and their combinations addition on natural gas fueled HCCI engine

Hydrogen, oxygen, and their combinations as effective species in the production of radical OH, which plays an effective role in the HCCI combustion enhancement, are considered to study their effect on combustion characteristics and resolving the challenges facing natural gas HCCI engines numerically. There are five items were considered for adding oxygen, hydrogen and their compounds, including 1%, 2%,3%, 4% and 5% of the fuel mixture for hydrogen, 10%, 20%, 30%, 40% and 50% for the extra oxygen in oxidizer and add up half of each respectively, including 0.5% H2 + 5%O2, 1% H2 + 10%O2, 1.5% H2 + 15%O2, 2% H2 + 20%O2, and 2.5% H2 + 25%O2. Adding hydrogen to some extent improves the engine efficiency, lowers combustion duration, and brings the engine cycle closer to the ideal Otto cycle and reduces CO and UHC emissions, but it can only increase engine operating range by as much as 4.2% at low load, increases NO emission, and increases the combustion noise. Hydrogen addition results in faster methane combustion, shortens the fuel combustion duration and increases the OH radical concentration. Up to 30%, added oxygen can extend the engine working range up to 48% at low loads, making the engine run smoother and shortening the combustion duration, although IMEP and efficiency decrease, CO and UHC emissions increase. By using hydrogen and oxygen compounds obtained their both benefits simultaneously, the engine operating range expands by 40.19% at low loads, the emissions would be less than the Euro 6 standard limitation and the maximum difference in efficiency is only 2.38% less than hydrogen addition. By adding these additives, ignition delay decreases and SOC advances. Using hydrogen and oxygen to improve engine performance at low loads is an appropriate and affordable solution, which does not cost much.

Selective catalytic reduction of NOx with NH3 and CH4 over zeolite supported indium-cerium bimetallic catalysts for lean-burn natural gas engines

Selective catalytic reduction (SCR) is recognized as an effective technology to control NOx emissions from lean-burn natural gas engines, but combining ammonia and methane as reductants for SCR of NOx has not been studied systematically. Herein, we investigated the SCR of NOx with NH3 and CH4 over InCeOx/HBEA catalysts. Different characterization methods were applied, including XPS, XRD, TPR, EPR, NMR, TEM, SEM, TPD and in-situ DRIFTS. The results reveal that the In8CeOx/HBEA catalyst presents high activity in a wide temperature range. Its NOx conversion, N2 selectivity and NH3 consumption are nearly 100% from 250 to 600 °C during the NH3/CH4-SCR process. Meanwhile, the In8CeOx/HBEA catalyst shows good tolerance to CO2, H2O and SO2. In addition, it was also found that NOx were mainly adsorbed on cerium species, and then oxidized to nitrite and nitrate species. NH3 is mainly adsorbed on the Bro¨nsted and lewis acid sites to form NH4+ and coordinated NH3 species. The ammonia nitrite and nitrate species are the main active intermediates for NH3-SCR. Meanwhile, methane is activated on InO+Z– sites, and then reacts with surface nitrate/nitrite species to form a short-lived intermediate nitromethane (CH3NO2) for CH4-SCR. Furthermore, a series of elementary steps are proposed to elucidate the SCR reaction mechanism. The fast NH3-SCR process is mainly responsible for NOx reduction in the low temperature range, and the standard NH3-SCR and CH4-SCR process are mainly responsible for NOx reduction in the high temperature range. These results show that In8CeOx/HBEA is a promising catalyst for the removal of NOx from natural gas fueled engines.

Sulfur poisoning and regeneration of Rh-ZSM-5 catalysts for total oxidation of methane

The activity of Rh/ZSM-5 catalysts for methane oxidation was investigated under conditions simulating the exhaust from lean burning, natural gas fueled engines to evaluate the influence of reaction atmosphere on catalytic activity. The Rh-catalysts yield high methane conversion at conditions achievable in real exhaust systems, despite the inhibiting effects of H2O and SO2. The influence of temperature and SO2 concentration (1−20 ppm) on the activity were studied. The deactivation caused by SO2 was intensified with decreasing temperature and increasing SO2 concentration, and the SO2-poisoning could be modeled as the occupation of active sites following a Temkin adsorption isotherm. At 400 °C essentially full coverage of S-species was reached with 1−2 ppm of SO2, but at 500 °C the coverage had decreased significantly, and considerable catalytic activity was preserved in the presence of SO2. Significant activity was regenerated in SO2-free gas, but the nature of the SO2-free regeneration atmosphere was unimportant.