Reformed Exhaust Gas Recirculation Research Articles

Fuel consumption and NOx emissions optimization of a marine natural gas engine with lean-burn and reformed exhaust gas recirculation strategies

Marine natural gas (NG) engines have received extensive attention in the shipping industry. To further improve the performance of the lean-burn engine, the reformed exhaust gas recirculation (REGR) technology which can realize hydrogen-rich combustion and exhaust gas recirculation is considered. In the present study, a comprehensive investigation on the performance of the marine NG engine with the exhaust gas-fuel reformer (the closed-loop system) was performed by GT-power software. Firstly, the characteristics of the reformer under different excess air ratios (λ) and reformate addition rates (Rre) were analyzed at specific M/O (the volume ratio of CH4 to O2 in the reformer inlet). Then, effects of the lean-burn strategy (the increase of λ) and REGR strategy (the increase of Rre) on combustion, performance and emission of the engine were studied. Moreover, the multi-objective genetic algorithm was utilized to obtain the optimal operating parameters (λ, Rre and M/O) of the closed-loop system. The results showed that the combustion duration is prolonged, the peak in-cylinder pressure and the NOx emissions are reduced with the increase of λ and Rre, but the brake specific fuel consumption (BSFC) is slightly increased. Despite the energy loss during the reforming process, BSFC of the engine with REGR strategy is lower than that of the lean-burn strategy due to the improvement of the engine thermal efficiency. Taking IMO’s Tier Ⅲ NOx standards and lowest BSFC as the optimization objects, the closed-loop system is recommended to work at λ = 1.41–1.49, Rre = 12–14%, and M/O = 1.0–1.2.

Effects of reformed exhaust gas recirculation (REGR) of ethanol-gasoline fuel blends on the combustion and emissions of gasoline direct injection (GDI) engine

Transportation is one of fast-growing sources of greenhouse gas emission worldwide. Road transport accounts as the main cause of HC, CO, NOX, CO2, and PM emissions. Ethanol blended fuel could improve engine performance and reduce both gaseous and PM emissions. Meanwhile, reformed exhaust gas recirculation (REGR) is introduced to achieve simultaneous reduction of NOX and PM from gasoline engines. In this work, the effect of REGR on combustion characteristics, and emissions of the gasoline direct injection (GDI) engine fuelled with ethanol-gasoline fuel blends (E10 and E20) was investigated. The H2 and CO mixture were used as a simulated REGR charge which was fed to the GDI engine’s intake manifold. The H2/CO ratio was determined via modelling of ethanol-gasoline fuel blend reforming based on equilibrium analysis. Moreover, the characteristics of PM emission (e.g. size distribution, primary particle size, morphology) were explored using TEM imaging. The results revealed that REGR could simultaneously improve both the engine thermal efficiency and engine-out emissions. A total number of PM particles and average primary particle size were reduced and compared with baseline (no-EGR) condition. An insight from this investigation can be used for designing control strategies to reduce the negative impact of internal combustion engine usage on human health and environment.

Hydrogen-rich gas generation via the exhaust gas-fuel reformer for the marine LNG engine

Reformed exhaust gas recirculation technology has attracted great attention in internal combustion engines. A platform of an exhaust gas-fuel reformer connected with the marine LNG engine was set up for generating on-board hydrogen. Based on the platform, effects of the methane to oxygen ratio (M/O) and reformed exhaust gas ratio (REG) from the reformer and excess air ratio (λ) from the engine on the components, hydrogen yield, thermal efficiency and reforming process of the reformer were experimentally investigated. Results shown that hydrogen-rich gases (reformate) can be generated by reforming the mixture of engine exhaust gas (about 400 °C) and methane supplied via the reformer with Ni/Al2O3 catalyst, and the hydrogen concentration of reformate was between 6.2% and 12.6% by volume. The methane supplied rate and λ affected the components and temperature of the reactant in the reformer, while REG changed the gas hour space velocity during the exhaust gas-fuel reforming processes, resulting in the difference in the components of the reformate and thermal efficiency. At the present experimental condition, the highest H2 concentration reformate was generated under the M/O of 2.0, λ of 1.55 and REG of 6%.

Application of reformed exhaust gas recirculation on marine LNG engines for NOx emission control

In the present study, the reformed exhaust gas recirculation (REGR) technique was employed on the marine engine fueled with LNG (i.e., marine LNG engine) for the reduction of emissions. A specially designed exhaust gas reformer was integrated with the marine LNG engine and then the performance of the closed-loop system of the reformer and engine was investigated, aiming at exploring the emissions reduction potential of the REGR technique for the marine LNG engine. The results showed that the NOx emission of the marine LNG engine with REGR was lower than that of the prototype engine by 60–70% and meanwhile can meet the Tier III emissions regulations. For the marine LNG engine with REGR, high rate of natural gas supplied to the reformer (RRNG) increased the concentrations of H2 and CO in the reformate. This advanced the flame speed of in-cylinder mixtures and led to a high peak pressure and heat release rate, resulting a 20–26% increase in NOx emission and a 10–12% decrease in the unburned hydrocarbon emission. Because of the variation in thermal efficiency of the reformer and engine, the fuel consumption rate of the closed-loop system showed a different trend with the increase of RRNG at different loads.

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 (Rre) 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 Rre, and the combustion efficiency is improved. The brake specific NOx emissions first increase and then decrease with the increase of Rre due to the competition between the combustion phase and total heat release value. The brake specific THC emissions decline with the increase of Rre, 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 NOx emissions and brake specific fuel consumption of the marine NG engine to meet the IMO Tier Ⅲ NOx emissions legislations and maintain relatively low brake specific fuel consumption.

Emission reduction using biodiesel blends with nano-additives and reformed exhaust gas recirculation (REGR) in DI diesel engine

Internal combustion engines are important contributors to environmental and human health hazardous air pollution. This research work Reformed Exhaust Gas Recirculation (REGR) is very acutely focused on the viability of using B20MEOJAO (Methyl Ester of Jatropha with nano-additive of aluminium oxide) in diesel as a blend, and its performance, emission and combustion characteristics were evaluated. The energy balance analysis was carried in all the blends. As a result, the performance and emission were improved. The brake thermal efficiency is 3% higher in B20MEOJAO30ppm blend compared to REGR. The oxides of nitrogen emission reduced in 25% REGR B20MEOJAO30ppm blend compared to without REGR in diesel and B20MEOJAO30ppm. The lower NOx is lower in B20MEOJAO30ppm 20% REGR compared to diesel and other ratios. The B20MEOJAO30ppm blend energy utilisation is closer to diesel.

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

Abstract 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, NOx 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.

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 (Rref) 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 Rref at high load, and therefore the total CH4 emissions decrease. However, the total CO emissions increase with the increase of Rref, 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 Rref 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.

Exploring the potential of reformed-exhaust gas recirculation (R-EGR) for increased efficiency of methanol fueled SI engines

Methanol is a promising fuel for spark ignition engines because of its high octane number, high octane sensitivity, high heat of vaporization and high laminar flame speed. To further boost the efficiency of methanol engines, the use of waste heat for driving fuel reforming was considered. This study explores the possibility of the reformed-exhaust gas recirculation (R-EGR) concept for increased efficiency of methanol engines. A simple Otto cycle calculation and a more detailed gas dynamic engine simulation are used to evaluate that potential. Both methodologies point to an enhancement in engine efficiency with fuel reforming compared to conventional EGR but not as much as the increase in lower heating value of the reforming product would suggest. A gas dynamic engine simulation shows a shortening of the flame development period and the combustion duration in line with the expected behavior with the hydrogen-rich reformer product gas. However, the heat loss increases with the presence of hydrogen in the reactants. The improvement of brake thermal efficiency is mainly attributed to the reduction of pumping work. The R-EGR concept is also evaluated for ethanol and iso-octane. As the reforming fraction increases, the efficiency of ethanol and iso-octane fueled engines rises faster than for the methanol engines due to a higher enhancement of exergy in their reforming products. At high reforming fractions, the efficiency of the ethanol engine becomes higher than with methanol. However, if the impact of optimal compression ratio for different fuels are considered, the methanol engine is able to produce a higher efficiency than the ethanol engine.

Computational Study of the Laminar Reaction Front Properties of Diluted Methanol–Air Flames Enriched by the Fuel Reforming Product

The current work investigates the flame structure and the propagation of premixed laminar flame fronts for mixtures of diluted methanol–air enriched by fuel reforming products under spark ignition engine conditions. Two engine concepts were investigated: one with external fuel reforming (EFR) and one with reformed exhaust gas recirculation (R-EGR). Here, the fuel reformate (or syngas) is a mixture of H2, CO, and CO2 with a CO selectivity of 6.5%, which is used to represent the products of methanol steam reforming over a Cu–Mn/Al foam catalyst. The simulations were exercised over a wide range of dilution level and unburned gas temperature at 40 bar with a skeletal chemical kinetic mechanism using zero/one-dimensional codes. Two types of dilution—air and EGR—were compared at the same fuel-to-charge equivalence ratio (ϕ′). The results showed that the knock limit for spark-ignited operation is extended with rising dilution levels, especially when diluted by an R-EGR mixture. Syngas addition also leads to a re...

Numerical study of combustion characteristics of a natural gas HCCI engine with closed loop exhaust-gas fuel reforming

In order to examine the potential of Natural Gas (NG) engines combining with reformed exhaust gas recirculation (REGR) system, a numerical study was carried out to investigate the combustion characteristics of a NG-HCCI engine with exhaust-gas fuel reforming by using CHEMKIN software. The results indicate that hydrogen added into the cylinder can range from 0.035 up to 0.16. At an equivalence ratio of 0.02 and exhaust gas recirculation (EGR) ratio of 0.2, the indicated mean pressure reaches the maximum and fuel consumption rate reaches the minimum. The hydrogen addition can advance combustion timing and improve the combustion efficiency. Since the exhaust gas offers not only heat but also a certain of CO, H2O, O2, etc., EGR ratio affects the initial conditions during the reforming processes which results in an obvious variation of hydrogen production. It is also found that, with the increase of H2 addition into the cylinder, the H atoms in cylinder is increased, which promotes the generation of H2O2 and the combustion of engine in advance and more intense. Furthermore, CO2 emission of the engine is affected by both the initial gas conditions in cylinder and the concentrations of CO and H atoms in the inlet gas of engine.

Effect of reformed EGR on the performance and emissions of a diesel engine: A numerical study

Diesel fueled CI engine is a widely accepted prime over owing to its high fuel conversion efficiency and load bearing capabilities. However, its use is constrained by high NOx and PM emissions. To address the issue of effective abatement of these emissions, an attempt is made in the present work and work reports numerical studies on the effect of reformed exhaust gas recirculation (REGR) of a single cylinder compression ignition engine fueled with diesel. For this purpose, a computational study using ECFM-3Z (extended coherent flame model-3 zones) model, ES-ICE and STAR-CD code has been carried out. Considering a sector model of an engine cylinder, in-cylinder pressures and temperatures Soot and Nitrous oxides (NOX) emission characteristics are observed. The studies include numerical experiments on various levels of REGR with two different compositions and comparison with their respective exhaust gas recirculation (EGR) levels at medium load conditions (write specific amounts). The REGR trends of combustion and emissions are significantly modified (is it correct here) when compared to EGR levels. Peak pressures for all REGR cases are higher than those for corresponding EGR levels. A maximum of 12.1% increase in peak pressure is found for 15% REGR (25%H2-0%CO) case than that for 15% EGR. Except for 25% REGR cases, Piston work for 5% REGR and 15% REGR cases is found to be higher than that for respective EGR because of H2 combustion dominance over exhaust gases dilution. Soot emissions for all REGR cases are observed lower than those for corresponding EGR cases. A maximum reduction of 12.73% is noted for 15% REGR (25%H2-0%CO) case than that for 15% EGR.

Numerical study of effects of reformed exhaust gas recirculation (REGR) on dimethyl ether HCCI combustion

The effects of reformed exhaust gas recirculation (REGR) on combustion and emissions of dimethyl ether (DME) homogeneous charge compression ignition (HCCI) engines are studied by multi-dimensional CFD coupled with chemical kinetic model. The results show that REGR combing EGR and DME reformed gases (DRG) improves combustion and emissions. REGR can delay ignition time by both EGR and DRG, and makes main combustion closer to top dead center (TDC), which is beneficial to reducing compression negative work and broadening load range of HCCI engines. The interaction of DRG and EGR helps avoid too high pressure rise rate or low power performance when being applied independent of each other. HC, CO and NOx emissions can be controlled simultaneously by REGR. Both advantages of DRG and EGR are used to decrease the emissions of HCCI engines by REGR, while the disadvantages of high emissions are alleviated when one of them is applied.

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).The REGR system was simulated by supplying hydrogen and carbon monoxide (CO) into a conventional EGR system. The hydrogen and CO concentrations in the REGR stream were selected to be achievable in practice at typical gasoline exhaust temperatures. Emphasis was placed on comparing REGR to the baseline gasoline engine, and also to conventional EGR. The results demonstrate the potential of REGR to simultaneously increase thermal efficiency, reduce gaseous emissions and decrease PM formation.

An Integrated System of Gasoline Reformer and Thee Way Converter for On-board hydrogen Production

On-board exhaust gas assisted gasoline reforming has been investigated using a compact prototype system consisting of a fuel reformer integrated with a three-way catalytic converter (TWC) connected to a V6 engine running at homogeneous charge compression ignition (HCCI) mode, the integrated fuel reformer, and TWC were designed and constructed to supply reformed exhaust gas recirculation (REGR) stream to the gasoline-fuelled HCCI V6 engine as supplement fuel to improve engine performance and reduce NOx emissions.To find the optimum operating conditions of the engine-reformer system (in terms of hydrogen production and thermal efficiency), the effect of oxygen to carbon ratio (O2/C) in the reactor input mixture, and the different engine operating conditions were investigated. The reactor outlet temperature appears to be strongly correlated to the production of hydrogen. Concentrations up to 12.8 % of hydrogen in the reformer products were achieved from commercial unleaded gasoline. Uncompleted reforming of gasoline was assumed from significant quantities of hydrocarbons in the product measured by Non-Dispersive Infrared (NDIR). The novel design of an integrated fuel reformer and three-way catalytic converter

Effects on CHP plant efficiency of H2 production through partial oxydation of natural gas over two group VIII metal catalysts

Blending H2 with natural gas in spark ignition engines can increase for electric efficiency. In-situ H2 production for spark ignition engines fuelled by natural gas has therefore been investigated recently, and reformed exhaust gas recirculation (RGR) has been identified a potentially advantageous approach: RGR uses the steam and O2 contained in exhaust gases under lean combustion, for reforming natural gas and producing H2, CO, and CO2. In this paper, an alternative approach is introduced: air gas reforming circulation (AGRC). AGRC uses directly the O2 contained in air, rendering the chemical pathway comparable to partial oxidation. Formulations based on palladium and platinum have been selected as potential catalysts. With AGRC, the concentrations of the constituents of the reformed gas are approximately 25% hydrogen, 10% carbon monoxide, 8% unconverted hydrocarbons and 55% nitrogen. Experimental results are presented for the electric efficiency and exhaust gas (CO and HC) composition of the overall system (SI engine equipped with AGRC). It is demonstrated that the electric efficiency can increase for specific ratios of air to natural gas over the catalyst. Although the electric efficiency gain with AGRC is modest at around 0.2%, AGRC can be cost effective because of its straightforward and inexpensive implementation. Misfiring and knock were both not observed in the tests reported here. Nevertheless, technical means of avoiding knock are described by adjusting the main flow of natural gas and the additional flow of AGRC.

Low-Load Dual-Fuel Compression Ignition (CI) Engine Operation with an On-Board Reformer and a Diesel Oxidation Catalyst: Effects on Engine Performance and Emissions

In the exhaust gas fuel-reforming method, part of the engine exhaust gas reacts with small amounts of engine fuel in a mini-reactor fitted in the exhaust gas recirculation (EGR) loop to produce gaseous fuel named reformed EGR (REGR). In this study, hot REGR (gas containing H2, CO, CH4, and CO2) was fed back to the engine inlet, so that the diesel engine in effect operated in dual fuel with inlet heating and EGR (CO2 existence). The effects of the diesel engine dual fueling with different REGR percentages on the engine performance and emissions have been examined. The study focused at low-load engine operation, where the conditions are not favorable for efficient gaseous fuel oxidation and engine combustion stability. The addition of the premixed gaseous fuel resulted in a remarkable reduction of both NOx and smoke engine emissions. Carbon monoxide and hydrogen oxidation efficiency can be improved by careful selection of REGR addition (e.g., premixed air/fuel ratio, inlet temperature, and reduced in-cylinder O2 concentration) and in-cylinder diesel injection timing. The use of Pt supported on Al2O3 as an oxidation catalyst at the engine exhaust can eliminate both CO and H2 at temperatures lower than the engine exhaust gas temperature at part loads. Preferably, in an actual engine reformer system, the uncombusted CO and H2 will be used to enhance the aftertreatment system (i.e., diesel particulate filter, NOx traps, and hydrocarbon-selective catalytic reduction of NOx) performance.

Partially premixed charge compression ignition engine with on-board [formula omitted] production by exhaust gas fuel reforming of diesel and biodiesel

The application of the exhaust gas fuel reforming process in diesel engines has been studied experimentally as a way to assist the premixed charge compression ignition operation by substituting part of the main fuel with hydrogen-rich gas. The technique involves the injection of hydrocarbon fuel into a catalytic reformer fitted into the exhaust gas recirculation (EGR) system, so that the produced gas mixture is fed back to the engine as reformed EGR (REGR). First, experiments with simulated REGR were conducted with diesel as well as biodiesel as the main engine fuel. Then, experiments with the product gas of a monolith reformer were carried out. In both cases, REGR resulted in a higher premixed combustion rate and reduction of the diffusion combustion phase. The potential of the technique in terms of achieving reduction of smoke and NO x emissions and improved fuel economy has been shown and discussed in the paper.