Hydrogen applications in selective catalytic reduction of NOx emissions from diesel engines

Diesel engines have been considered as a major source in nitrogen oxide (NO_x) formation worldwide. The widespread use of diesel engines in consequence of their low fuel consumption, high durability and efficiency increases NO_x emissions day by day. NO_x emissions from diesel engines cause unavoidable damage on environment and people health. Although so many technologies such as exhaust gas recirculation (EGR), lean burn combustion, electronic controlling fuel injection systems, etc. have been developed to control NO_x emissions from diesel engines, they couldn't meet the desired reduction in NO_x emissions. In any case, Selective Catalytic Reduction (SCR) as one of the most promising aftertreatment-emission control technologies is an effective solution in restriction of NO_x emissions. The use of SCR systems especially in heavy-duty diesel powered vehicles has been increasing nowadays. In these systems, to use of hydrogen (H₂) as a reductant or promoter have been improved the conversion efficiency especially at low exhaust temperatures. Many researchers have been focused on the use of H₂ in SCR systems for controlling NO_x emissions.In this study, the applications of H₂ in SCR of NO_x have been discussed. The studies on use of H₂ in SCR of NO_x emissions were examined and the effects on NO_x conversions were determined. Consequently, it is confirmed that H₂ is a promising and alternative reductant in SCR of NO_x and it has been kept as an attracting subject for many researchers.     

NOx emission from a two-stroke ship engine. Part 1: Modeling aspect

International Maritime Organization regulations forces ship owners to measure NO_x emission from ship engines, but standard equipped engine rooms has not installed any usable apparatus to analyze of exhaust gases. In this paper, we propose a method of NO_x emission estimation based on the measurements of working parameters of two-stroke ship engine. This estimation consists of both the model enabling to determine a temperature and model of composition of a gas mixture in the combustion chamber of the engine. Application of such model does not require carrying out direct measurements of engine exhaust gases by exhaust gas analyzers. For the developed method, results of engine working parameters should be sufficient to estimate the NO_x emission according to IMO regulations.     

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.     

船用低速柴油机低压SCR系统台架试验研究

结合船用低速柴油机的技术特点设计了低压SCR系统并开展了台架试验研究。试验结果表明:所设计的SCR系统NO_x减排效果明显,NH₃逃逸量较小,满足相关法规要求;柴油机在加装SCR系统后排气压力损失满足设计要求,且对燃油消耗率影响较小。     

The influence of hydrogen-enriched gas on the performance of lean NOx trap catalyst for a light-duty diesel engine

Modern diesel engines have improved engine fuel economy and significantly reduced nitrogen oxides (NO_x) and particulate matter (PM) emissions achieved by advances in both combustion and exhaust aftertreatment technologies. Recently, it has been shown that the vehicle emissions can be further improved by several catalytic systems including fuel reformers and aftertreatment systems, such as the Lean NO_x Trap (LNT). This NO_x removal system, called LNT, absorbs NO_x under lean exhaust gas conditions and releases NO_x under rich conditions. This technology can provide high NO_x conversion efficiency, but the right amount of reducing agent should be supplied into the catalytic converter under appropriate conditions.     

Promoting hydrocarbon-SCR of NOx in diesel engine exhaust by hydrogen and fuel reforming

A hydrocarbon-selective catalytic reduction (HC-SCR) silver–alumina monolith catalyst has been prepared and tested for NO_x emissions control in a diesel engine. The work is based on ongoing laboratory experiments, catalyst research, and process development. Hydrogen and actual reformate (i.e. H₂ and hydrocarbon species produced in a partial and exhaust gas fuel reformer) significantly improved the passive control (i.e. no externally added hydrocarbons) NO_x reduction activity over the SCR catalyst using the whole engine exhaust gas from a single-cylinder diesel engine. Optimisation of the reforming process is required for various engine conditions in order to maximise H₂ production and minimise fuel penalty. When diesel fuel partial oxidation and exhaust gas reforming for SCR were implemented, the calculated fuel penalty was in the range of 5–10%, which is relatively high, as both reformers were not optimised yet. During HC-SCR of NO_x over silver–alumina, the known promoting effect of H₂ has been found to be sensitive to various factors, especially the engine exhaust gas temperature, H₂ concentration, HC concentration, HC:NO_x ratio, and space velocity. Under active control (i.e. hydrocarbon injection) SCR operation, powdered Ag–Al₂O₃ catalysts gave significantly higher initial NO_x reduction, but the catalyst activity deteriorated rapidly with time due to poisoning species adsorption (e.g. HCs, nitrates, particulate matter (PM), etc.), whilst for the Ag–Al₂O₃-coated monolithic catalysts, NO_x reduction activity was lower but remained constant for the duration of the tests. The improved physical (mass transfer, filtering of C-containing species) and chemical (reaction kinetics) processes during HC-SCR over powders compared to monoliths led to better initial catalyst activity, but it also accelerated catalyst deactivation which led to increased diffusion limitations.     

Evaluation of carbon nanotubes produced from toluene steam reforming as catalyst support for selective catalytic reduction of NOx

There is current interest in developing low cost, effective catalysts for the low temperature selective catalytic reduction (SCR) of nitrogen oxides (NO_x). In this work, we have applied carbon nanotubes (CNTs), produced as a by-product of hydrogen production from the steam reforming of toluene (as a representative hydrocarbon), as a catalyst support for a V₂O₅–WO₃ catalyst for SCR of NO_x. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis showed well dispersed metals on the surface of the CNTs. The V₂O₅–WO₃/CNT catalyst has exhibited NO_x reduction efficiency higher than 95% at reaction temperatures between 340 and 400 °C. However, there was a low NO_x reduction at SCR reaction temperature of less than 200 °C which is suggested to be due to the lack of Lewis acid sites, as determined from NH₃-TPD (temperature program desorption) analysis. Future work to lower the SCR reaction temperature with high NO_x efficiency is suggested.     

Investigation of a hydrogen-assisted combustion system for a light-duty diesel vehicle

Two sets of experiments were conducted to investigate the effects of adding gaseous hydrogen to the intake of compression–ignition (CI) engines fueled with 20% bio-derived/80% petroleum-derived diesel fuel (B20). A 1.3 L, 53 kW CI engine coupled to an eddy-current engine dynamometer was tested first. Data were collected on engine operating parameters, fuel consumption, concentration of total oxides of nitrogen (NO_x) in the exhaust, and exhaust temperature. Eight steady-state operating points were tested with hydrogen flow rates equivalent to 0%, 5%, and 10% of the total fuel energy. In a second set of experiments, the stock gasoline engine of a 2005 Chevrolet Equinox was replaced with a 1.3 L, 66 kW CI engine, and urban drive cycles were run on a chassis dynamometer. The drive cycles were repeated with 0%, 5% and 10% of the fuel energy coming from the fumigated hydrogen. In both experiments, the addition of hydrogen did not result in discernable differences in engine efficiency. In the vehicle testing, there were no noticeable differences in drivability. There were modest reductions in NO_x emissions and increases in exhaust temperature with hydrogen addition. This investigation demonstrates that fumigating relatively small amounts of hydrogen into the intake of a modern diesel engine results in only modest changes in combustion efficiency and emissions with no detrimental effects on vehicle performance or drivability. This strategy can be used to partially offset the use of petroleum-based fuels in light-duty transportation vehicles.     

Catalytic reduction of NOx in gasoline engine exhaust over copper- and nickel-exchanged X–zeolite catalysts

Catalytic removal of NO_x in engine exhaust gases can be accomplished by non-selective reduction, selective reduction and decomposition. Noble metals are extensively used for non-selective reduction of NO_x and up to 90% of engine NO_x emissions can be reduced in a stoichiometric exhaust. This requirement of having the stoichiometric fuel–air ratio acts against efficiency improvement of engines. Selective NO_x reduction in the presence of different reductants such as, NH₃, urea or hydrocarbons, requires close control of the amount of reductant being injected which otherwise may be emitted as a pollutant. Catalytic decomposition is the best option for NO_x removal. Nevertheless, catalysts which are durable, economic and active for NO_x reduction at normal engine exhaust temperature ranges are still being investigated.Three catalysts based on X–zeolite have been developed by exchanging the Na⁺ ion with copper, nickel and copper–nickel metal ions and applied to the exhaust of a stationary gasoline engine to explore their potential for catalytic reduction of NO_x under a wide range of engine and exhaust conditions. Some encouraging results have been obtained. The catalyst Cu–X exhibits much better NO_x reduction performance at any temperature in comparison to Cu–Ni–X and Ni–X; while Cu–Ni–X catalyst exhibits slightly better performance than Ni–X catalyst. Maximum NO_x conversion efficiency achieved with Cu–X catalyst is 59.2% at a space velocity (sv) of 31 000 h⁻¹; while for Cu–Ni–X and Ni–X catalysts the equivalent numbers are 60.4% and 56% respectively at a sv of 22 000 h⁻¹. Unlike noble metals, the doped X–zeolite catalysts exhibit significant NO_x reduction capability for a wide range of air/fuel ratio and with a slower rate of decline as well with increase in air/fuel ratio.     

Environmental evaluation of introducing electric vehicles using a dynamic traffic-flow model

A dynamic traffic-flow model (DTFM) is used in this study to evaluate the effectiveness of introducing electric vehicles (EVs) into the total traffic system as one of the alternative fuel vehicles. This model simulates congested and non-congested traffic flow caused by changes in the traffic demand. An environmental evaluation is carried out on the basis that all vehicles are substituted for EVs. Calculated results indicate that by introducing EVs, the NO_x emissions and the CO₂ emissions can be reduced by approximately 25.7 and 14.4% respectively. If battery performance of EVs is improved further, emissions can be further reduced by 39.6% (NO_x) and 27.8% (CO₂). Since emissions from heavy-duty vehicles are greater than other vehicles, the following measures have to be taken for these vehicles to significantly improve their impact upon the overall environment: (1) improvement in fuel efficiency and reductions of NO_x in exhaust gas, (2) traffic demand management, such as modal shift.     

Performance and combustion characteristics of alcohol–gasoline blends at wide-open throttle

This study discusses the performance and exhaust emissions of a vehicle fueled with low content alcohol (ethanol and methanol) blends and pure gasoline. The vehicle tests were performed at wide-open throttle and at vehicle speeds of 40 km h⁻¹, 60 km h⁻¹, 80 km h⁻¹ and 100 km h⁻¹ by using an eddy current chassis dynamometer. The test results obtained with the use of alcohol-gasoline blends (5 and 10 percent alcohol by volume) were compared to pure gasoline test results. The test results indicated that when the vehicle was fueled with alcohol-gasoline blends, the peak wheel power and fuel consumption slightly increased. And also, in general, alcohol-gasoline blends provided higher combustion efficiency compared to pure gasoline use. In exhaust emission results, a stable trend was not seen, especially for CO emission. But, on average, alcohol-gasoline blends exhibited decreasing HC emissions. In 100 km h⁻¹ vehicle speed test, the alcohol-gasoline blends provided lower vehicle performance and lower NO_x emission values compared to pure gasoline. At all vehicle speeds, minimum CO₂ emission was obtained when 5% methanol was added in gasoline. The low content alcohol blends did not reveal any starting problem, or irregular operation on the engine.     

Energy use,industrial soot and vehicle exhaust pollution—China's regional air pollution recognition,performance decomposition and governance

The identification of “industrial soot” or “vehicle exhaust” pollution facilitates developing proper measures for the mitigation of regional air pollution. In order to identify the pollution types at a regional level, this paper applies the Luenberger productivity indicator to decompose air pollutant emissions performance. Furthermore, we simultaneously consider pollution rates and the productivity change. Thus, we propose a new modeling framework allowing for the variable-specific decomposition of the environmental performance along time and quantity dimensions to identify the underlying patterns. The panel data for 30 provinces and autonomous regions are then applied to identify regional atmospheric pollution type. The results show that SO₂ emission from industrial soot and NO_x emissions from vehicle exhaust constitute an important source of regional atmospheric environmental inefficiency, though the former seems to be more decisive. The southeast coastal provinces showed generally lower levels of inefficiency, compared to the northwest inland area. During the period of the 11th Five-Year Plan of China, industrial SO₂ emission performance contributed to the increase in the atmospheric environmental productivity, while traffic NO_x emissions acted as a negative factor in this regard. Therefore, the government should seek to increase the intensity of environmental regulation in transportation sector. At the country level, technical progress associated with both types of pollutions was positive and thus exceed the negative efficiency change for the same variables. In particular, in Beijing-Tianjin-Hebei region, the productivity changes in industrial SO₂ emissions and traffic NO_x emissions indicate a “stably advancing” type. The results further indicate that there are 18 provinces of China which have experienced mixed-type pollution. Jilin and Hainan were classified as provinces experiencing vehicle exhaust gas pollution, whereas Guizhou was defined as that subject to industrial soot pollution. The government should formulate and implement diversified support and regulation policies to govern SO₂ and NO_x pollution at the regional level.     

Effects of compression ratio on performance and emission characteristics of heavy-duty SI engine fuelled with HCNG

The wide range of hydrogen's flammable limits enables ultra-lean combustion. A lean burn reduces the combustion temperature, increases thermal efficiency, and reduces knock, which is a serious problem in a spark ignition (SI) engine. The anti-knock improvement from hydrogen addition makes it feasible to increase the compression ratio (CR) and further improve the thermal efficiency. Herein, the effects of the CR on performance and emission characteristics were investigated using an 11-L heavy-duty SI engine fuelled with HCNG30 (CNG 70 vol%, hydrogen 30 vol%) and CNG. These fuels were used to operate an engine with CRs of 10.5 and 11.5. The results showed that thermal efficiency improved with an increased CR, which significantly decreased CO₂ emission. On the other hand, the NO_x emission was largely increased. Nevertheless, for HCNG30, a CR of 11.5 improved thermal efficiency by 6.5% and decreased NO_x emission by over 75%, as compared to a conventional CNG engine.     

Exhaust emissions control and engine parameters optimization using artificial neural network virtual sensors for a hydrogen-powered vehicle

This paper presents an alternative tool for vehicle tuning applications by incorporating the use of artificial neural network (ANN) virtual sensors for a hydrogen-powered car. The objective of this study is to optimize simple engine process parameters to regulate the exhaust emissions. The engine process parameters (throttle position, lambda, ignition advance and injection angle) and the exhaust emission variables (CO, CO₂, HC and NO_x) form the basis of the virtual sensors. Experimental data were first obtained through a comprehensive experimental and tuning procedure for neural network training and validation. The optimization layer-by-layer neural network was used to construct two ANN virtual sensors; the engine and emissions models. The performance and accuracy of the proposed virtual sensors were found to be acceptable with the maximum predictive mean relative errors of 0.65%. With its accurate predictive capability, the virtual sensors were then employed and simulated as a measurement tool for vehicle tuning and optimization. Simulation results showed that the exhaust emissions can be regulated by optimizing simple engine process parameters. This study presents an alternative tool for vehicle tuning applications for a hydrogen-powered vehicle. In addition, this work also provided a tool to better understand the effects of various engine conditions on the exhaust emissions without the need for any vehicle modifications.     

Impact assessment of road fleet transitions on emissions: The case study of a medium European size country

This paper aims to examine the impacts of fleet composition changes on emission due to the introduction of different road transportation policies in a medium size European country (Portugal) applying an ex-post analysis (e.g. policies based on fuel pricing, car scraping, car taxation). A baseline scenario was compared with a counterfactual scenario in order to understand what would occur in the absence of the introduction of those policies. For each scenario, four approaches were assessed using economic effects and/or human health costs. HC, CO, NO_x, PM and CO₂ emissions from passenger cars and light duty vehicles were evaluated. The results show high statistical significance (p≤0.05) between CO emissions and different vehicle features as vehicle age, fuel type and engine classes. The same pattern was observed between the average vehicle age and HC, NO_x and PM. After the implementation of road traffic policies, the average emission factors of the fleet decreased 28–62% for HC, CO, NO_x, PM and 20–39% for CO₂. However, if a counterfactual scenario would be implemented, the reduction would be 20–80% and 26–55% higher, respectively. The results demonstrates that although were recorded some benefits, the fleet characteristics distribution were more environmental friendly in 2001 than in 2011.     

Effect of Exhaust Gas Recirculation (EGR) on performance,emissions, deposits and durability of a constant speed compression ignition engine

To meet stringent vehicular exhaust emission norms worldwide, several exhaust pre-treatment and post-treatment techniques have been employed in modern engines. Exhaust Gas Recirculation (EGR) is a pre-treatment technique, which is being used widely to reduce and control the oxides of nitrogen (NO_x) emission from diesel engines. EGR controls the NO_x because it lowers oxygen concentration and flame temperature of the working fluid in the combustion chamber. However, the use of EGR leads to a trade-off in terms of soot emissions. Higher soot generated by EGR leads to long-term usage problems inside the engines such as higher carbon deposits, lubricating oil degradation and enhanced engine wear. Present experimental study has been carried out to investigate the effect of EGR on soot deposits, and wear of vital engine parts, especially piston rings, apart from performance and emissions in a two cylinder, air cooled, constant speed direct injection diesel engine, which is typically used in agricultural farm machinery and decentralized captive power generation. Such engines are normally not operated with EGR. The experiments were carried out to experimentally evaluate the performance and emissions for different EGR rates of the engine. Emissions of hydrocarbons (HC), NO_x, carbon monoxide (CO), exhaust gas temperature, and smoke opacity of the exhaust gas etc. were measured. Performance parameters such as thermal efficiency, brake specific fuel consumption (BSFC) were calculated. Reduction in NO_x and exhaust gas temperature were observed but emissions of particulate matter (PM), HC, and CO were found to have increased with usage of EGR. The engine was operated for 96 h in normal running conditions and the deposits on vital engine parts were assessed. The engine was again operated for 96 h with EGR and similar observations were recorded. Higher carbon deposits were observed on the engine parts operating with EGR. Higher wear of piston rings was also observed for engine operated with EGR.     

NOx emission from a two-stroke ship engine: Part 2 – Laboratory test

International regulations force ship owners to monitor the NO_x emission from engines during sea operational use of ships, but standard equipped engine rooms has not installed any measurement equipment to analyze of exhaust gases. According to these regulations, we proposed a simple method to estimation of NO_x emission without direct measurement, based on the measurements of working engine parameters. In this paper, we present the effect of laboratory test to verification adequacy of the developed model. In this aim, we carried out tests on the two-stroke, one-cylinder, and loop scavenged diesel engine. During tests the engine operated with the various rotational speed, load, and changing air/fuel equivalence ratio. The comparison of the results of calculations with conducted tests showed the estimation errors in intervals 1.8% to 11% in dependence from the substitute molar compositions of fuels.     

Effects of acoustic excitation on pinch-off flame structure and NOx emissions in H2/CH4 flame

The flame structure and exhaust emissions of pinch-off flames, in which flames are separated under acoustic excitation conditions, were studied. Flame structure analysis was performed using OH1 chemiluminescence measurements, and exhaust emissions analysis was performed with a gas analyzer. Structure analysis of the pinch-off flame for acoustic excitation was performed basis the OH1 images, and various structures were confirmed according to the forcing frequency and velocity perturbation intensity. To analyze the correlation between the flame structure and NO_x emission, the flame residence time and emission index of NO_x (EINO_x) were analyzed according to the Strouhal number. The flame residence time and EINO_x decreased as the velocity perturbation intensity increased; analyzing the NO_x emission characteristics is limited when based only on the flame residence time. 1/2-power scaling was followed by EINO_x analysis and the Strouhal number was normalized to the flame residence time.     

An analytic study of applying Miller cycle to reduce NOx emission from petrol engine

An analytic investigation of applying Miller cycle to reduce nitrogen oxides (NO_x) emissions from a petrol engine is carried out. The Miller cycle used in the investigation is a late intake valve closing version. A detailed thermodynamic analysis of the cycle is presented. A comparison of the characters of Miller cycle with Otto cycle is presented. From the results of thermodynamic analyses, it can be seen that the application of Miller cycle is able to reduce the compression pressure and temperature in the cylinder at the end of compression stroke. Therefore, it lowers down the combustion temperature and NO_x formation in engine cylinder. These results in a lower exhaust temperature and less NO_x emissions compared with that of Otto cycle. The analytic results also show that Miller cycle ratio is a main factor to influence the combustion temperature, and then the NO_x emissions and the exhaust temperature. The results from the analytic study are used to analyse and to compare with the previous experimental results. An empirical formula from the previous experimental results that showed the relation of NO_x emissions with the exhaust temperature at different engine speed is presented. The results from the study showed that the application of Miller cycle may reduce NO_x emissions from petrol engine.     

Combustion performance and emission reduction characteristics of automotive DME engine system

This article is a condensed overview of a dimethyl ether (DME) fuel application for a compression ignition diesel engine. In this review article, the spray, atomization, combustion and exhaust emissions characteristics from a DME-fueled engine are described, as well as the fundamental fuel properties including the vapor pressure, kinematic viscosity, cetane number, and the bulk modulus. DME fuel exists as gas phase at atmospheric state and it must be pressurized to supply the liquid DME to fuel injection system. In addition, DME-fueled engine needs the modification of fuel supply and injection system because the low viscosity of DME caused the leakage. Different fuel properties such as low density, viscosity and higher vapor pressure compared to diesel fuel induced the shorter spray tip penetration, wider cone angle, and smaller droplet size than diesel fuel. The ignition of DME fuel in combustion chamber starts in advance compared to diesel or biodiesel fueled compression ignition engine due to higher cetane number than diesel and biodiesel fuels. In addition, DME combustion is soot-free since it has no carbon–carbon bonds, and has lower HC and CO emissions than that of diesel combustion. The NO_x emission from DME-fueled combustion can be reduced by the application of EGR (exhaust gas recirculation). This article also describes various technologies to reduce NO_x emission from DME-fueled engines, such as the multiple injection strategy and premixed combustion. Finally, the development trends of DME-fueled vehicle are described with various experimental results and discussion for fuel properties, spray atomization characteristics, combustion performance, and exhaust emissions characteristics of DME fuel.