Browse Topic: Fuel reformers
ABSTRACT This paper summarizes development and demonstration of F-24/JP-8-fueled Fuel-Cell Electric-Vehicle that offers silent-mobility, silent-watch, and export-power. The prototype electric vehicle was fueled with MIL-SPEC F-24/JP-8. It can potentially be operated with other logistic fuels and does not require onboard hydrogen storage. An onboard fuel reformer with integrated sulfur trap was used for processing MIL-SPEC F-24/JP-8. The 10-kW electric (kWe) generator included a solid oxide fuel cell and balance of plant components (oxidizer, pumps, blowers, sensors, power and control electronics). It was hybridized with a rechargeable battery for startup, peak loads, and load following. Water neutrality and silent operation (i.e., ~60 dBA at 1-meter) was confirmed. The power produced was sufficient for vehicle propulsion and export power. Both 28-32 VDC and 110 VAC for charging batteries and supporting external load demands were available onboard. Initial off-road demonstrations were conducted at PCI and Detroit Arsenal. System design and performance data are shared in the paper.
In prior work, the EGR loop catalytic reforming strategy developed by ORNL has been shown to provide a relative brake engine efficiency increase of more than 6% by minimizing the thermodynamic expense of the reforming processes, and in some cases achieving thermochemical recuperation (TCR), a form of waste heat recovery where waste heat is converted to usable chemical energy. In doing so, the EGR dilution limit was extended beyond 35% under stoichiometric conditions. In this investigation, a Microlith®-based metal-supported reforming catalyst (developed by Precision Combustion, Inc. (PCI)) was used to reform the parent fuel in a thermodynamically efficient manner into products rich in H2 and CO. We were able to expand the speed and load ranges relative to previous investigations: from 1,500 to 2,500 rpm, and from 2 to 14 bar break mean effective pressure (BMEP). Experiments were conducted to determine the effects of the H/C ratio of the fuel on H2 production and on the engine efficiency in order to compare E10 gasoline (H/C = 1.95) and liquified petroleum gas (LPG), comprised primarily of propane (H/C = 2.67). Additionally, the compression ratio of the engine was increased to ascertain whether further efficiency improvements could be realized based on a reduced knock propensity of the dilute EGR mixture with the reformed fuel. Both the gasoline and propane reforming strategies provided efficiency gains up to 1.85 percentage points and further efficiency improvements with the increased compression ratio were realized. The fuel specific effects of gasoline vs. LPG, the effect of engine operating condition on reforming, and knock limits of the reformed mixture are discussed in detail.
Methanol is a promising fuel for future spark-ignition engines. Its properties enable increased engine efficiency. Moreover, the ease with which methanol can be reformed, using waste exhaust heat, potentially offers a pathway to even higher efficiencies. The primary objective of this study was to build and validate a model for a methanol fueled direct-injection spark-ignition engine with on-board fuel reforming for future investigation and optimization. The second objective was to understand the combustion characteristics, energy losses and engine efficiency. The base engine model was developed and calibrated before adding a reformed-exhaust gas recirculation system (R-EGR). A newly developed laminar burning velocity correlation with universal dilution term was implemented into the model to predict the laminar burning velocity with the presence of hydrogen in the reforming products. At the same EGR ratio, there is a small increase in the engine efficiency with fuel reforming compared to conventional EGR. This is mainly due to the reduction of pumping work. For the R-EGR cases, around 60% of the increase in the brake efficiency is due to the reduction of pumping work. Although the increase in brake efficiency is very small, the maximum brake thermal efficiency for the R-EGR cases is higher than for the conventional EGR cases due to a significant increase in the dilution limit. With R-EGR dilution, the maximum brake thermal efficiency was found to increase by 6.9% relative to the baseline case.
A fuel reforming technology using a low temperature oxidation was developed to improve a NOx reduction performance of HC-SCR (Hydrocarbons Selective Catalytic Reduction) system, which does not require urea. The low-temperature oxidization of a diesel fuel in gas phase produces NOx reduction agents with high NOx reduction ability such as aldehydes and ketones. A pre-evaporation-premixing-type reformer was adopted in order to generate a uniform temperature field and a uniform fuel/air premixed gas, and to promote the low temperature oxidation efficiently. As a fundamental study, elementary reaction analysis for n-hexadecane/air premixtures was carried out to investigate the suitable reformer temperature and fuel/air equivalence ratio for generation of oxygenated hydrocarbons. It was found that the reforming efficiency was highest at the reforming temperature around 623 to 673K, and aldehydes and ketones were produced. It was inferred that the NOx reduction performance by the reformed fuel was higher than diesel fuel itself. The FTIR measurements of reformed-fuel-vapor composition and the experiments of NOx reduction in the catalyst temperature range of 473 K to 773 K were performed for n-hexadecane and diesel fuel using the developed reformer. A Ag/Al2O3 catalyst was used as the NOx reduction catalyst. As a result of composition analysis, it was confirmed that low-temperature oxidization of hydrocarbons occurred in the reformer as estimated by the elementary reaction analysis. The NOx reduction efficiency by reformed diesel fuel vapor was up to about 90%. Improvements of the efficiency of diesel fuel reforming and the NOx reduction performance in wide range of the catalyst temperature are challenges.
As global climate change concerns lead the automotive industry to push towards manufacturing more sustainable automobiles, a number of technologies and powertrains have developed. Less common among these new powertrains are fuel cell systems due to their relatively high cost and requirement of an associated fuel reformation process. This reformer is needed if widely available hydrocarbon fuels are to be used. There are currently few initiatives combining fuel cell systems with internal combustion engines, but these initiatives are unable to mitigate the primary drawbacks of fuel cell systems. Current designs place the engine downstream of the fuel cells, resulting in the same need for prior fuel processing. In this work, a configuration is considered in which the engine is placed upstream of the fuel cell system, and its syngas-rich exhaust is fed directly into the fuel cell system for electricity production. Fuel-rich compression-ignition engine combustion can break down fuel into hydrogen and carbon monoxide (syngas) and other minute hydrocarbon byproducts. Based on chemical kinetic model simulations, the composition of the syngas resulting from the fuel-rich combustion can be used to design test syngas compositions for the fuel cell system. The performance of micro-tubular solid oxide fuel cells (μT-SOFC) using this model exhaust as the primary fuel supply was then investigated. The SOFC was able to generate ~730 mW/cm2 on the model exhaust which corresponds to about ~86 % of the maximum power output obtained by fueling it with pure hydrogen. This demonstrates the potential of the suggested integration of an SOFC system with an internal combustion engine. Additionally, practical fuel-rich combustion in a combustion chamber and in a diesel engine was carried out to test and validate the simulated exhaust syngas composition. This promising innovative compact energy system eliminates both the need for fuel processing catalysts and the heating requirement for complex fuel reformers. It can be a more cost-effective high-efficiency solution than existing combined fuel cell system solutions.
A high temperature and no oxygen atmosphere fuel reforming has been proposed for the purpose of exergy saving by theoretical analyzing the detailed exergy loss events of combustion process, the correctness and feasibility of this fuel reforming have been verified through experiments. The exergy behaviors of high temperature and no oxygen atmosphere fuel reforming have been extensively studied, and many benefits had been observed including: (1) simplifying the reforming device where catalysts are not necessary; (2) improving the total chemical exergy while effectively converting large moleculae to small moleculae; (3) improving the mixture’s ratio of specific heat that can promote work-extraction; and (4) lengthening the ignition delay that buys time for better mixing process. All of these benefits are conducive to a better organized HCCI combustion that may improve the engine second law efficiency.
The Dual-Fuel (DF) combustion is a promising technology for efficient, low NOx and low exhaust particulate matter (PM) engine operation. To achieve equivalent performance to a DF engine with only the use of conventional liquid fuel, this study proposes the implementation of an on-board fuel reformation process by piston compression. For concept verification, DF combustion tests with representative reformed gas components were conducted. Based on the results, the controllability of the reformed gas composition by variations in the operating conditions of the reformer cylinder were discussed.
Onboard reforming has been proposed as a strategy for improving spark-ignited (SI) engine efficiency through knock reduction, dilution limit extension, improved thermodynamic gas properties, and thermochemical exhaust enthalpy recuperation. One approach to onboard fuel reforming is to combust fuel in the engine cylinder under rich conditions, producing a hydrogen-rich reformate gas--which can subsequently be recirculated into the engine. Hydrogen is the preferred product in this process due to its high flame speed and knock resistance, compared with other reformate constituents. In this work, the effects of engine operation, fuel composition and water injection were evaluated for their effect on reformate gas composition produced under rich combustion conditions. Engine parameters, including intake pressure, intake temperature, combustion phasing, and valve timing all had no significant impact on hydrogen yield at a given equivalence ratio. Fuel effects on hydrogen yield were more significant--with methanol producing 75% more hydrogen than toluene at the same equivalence ratio. The greater hydrogen yield was due to greater hydrogen content of the fuel, although the benefit was shown to be partially offset by lower hydrogen selectivity and conversion. Production of smoke limited the minimum relative air-fuel ratio of some fuels contributing to reduced hydrogen yields. Upstream water injection was shown to boost hydrogen production by 10-60% (rel.) at the expense of carbon monoxide due to steam reforming reactions and Le Chatlier’s principle in the water gas shift reaction. Toluene exhibited the greatest relative improvement in hydrogen yield due to the lower exhaust water concentrations in the absence of water injection. In the presence of water injection, hydrogen production in some cases exceeded fuel hydrogen content indicating the presence of water gas shift and steam reforming chemistry occurring. Using the speciated exhaust data, a correlation was developed using measured exhaust hydrogen content to predict hydrogen concentration from carbon monoxide and relative air-fuel ratio. The correlation developed improves upon previous correlations by explicitly including the hydrogen content of the fuel, and thus allowing more accurate prediction. Lastly, the energy balance was calculated under rich combustion conditions from the indicated power and chemical potential energy of the reformate. The energy balance analysis suggests that in-cylinder reforming is a net endothermic process, with some exhaust heat being converted into chemical potential energy. Overall, it was concluded that in-cylinder reforming can be used to produce practical quantities of reformate to improve SI engine performance. This work showed the potential for optimized fuels to improve in-cylinder reforming processes, in conjunction with water injection, to produce a hydrogen-rich reformate gas without parasitic losses.
Powertrain simulations and catalyst studies showed the efficiency credits and feasibility of onboard reforming as a way to recover waste heat from heavy duty vehicles (HDVs) fueled by natural gas (NG). Onboard reforming involves 1) injecting NG into the exhaust gas recycle (EGR) loop of the HDV, 2) reforming NG on a catalyst in the EGR loop to hydrogen and carbon monoxide, and 3) combusting the reformed fuel in the engine. The reformed fuel has increased heating value (4-10% higher LHV) and flame speed over NG, allowing stable flames in spark ignition (SI) engines at EGR levels up to 25-30%. A sulfur-tolerant reforming catalyst was shown to reform a significant amount of NG (15-30% conversion) using amounts of precious metal near the current practice for HDV emissions control (10 g rhodium). Engine simulations showed that the high EGR levels enabled by onboard reforming are used most effectively to control engine load instead of waste-gating or throttling. This leads to 3% efficiency gain due to reduced pumping losses and enables the engine to run while the catalyst is inactive, such as during a cold start or regeneration. Several powertrain layouts were assessed to show that a net efficiency gain of 10% is achievable when reforming occurs in a reactor that allows heat exchange with the non-recycled exhaust. The size of the heat exchange reactor was shown to be (4 ft. length, 7-10 in. diameter). The next steps to achieve onboard reforming include the development of the heat exchange reactor and validation with real engine testing.
In order to achieve high-efficiency and clean combustion in HCCI engines, combustion must be controlled reasonably. A great variety of species with various reactivities can be produced through low temperature oxidation of fuels, which offers possible solutions to the problem of controlling in-cylinder mixture reactivity to accommodate changes in the operating conditions. In this work, in-cylinder combustion characteristics with low temperature reforming (LTR) were investigated in an optical engine fueled with low octane number fuel. LTR was achieved through low temperature oxidation of fuels in a reformer (flow reactor), and then LTR products (oxidation products) were fed into the engine to alter the charge reactivity. Primary Reference Fuels (blended fuel of n-heptane and iso-octane, PRFs) are often used to investigate the effects of octane number on combustion characteristics in engines. Then PRF0 (n-heptane) and PRF50 (mixture of 50% n-heptane and 50% iso-octane by volume) were chosen as representative low octane number fuels. LTR products were quantitatively detected using online gas chromatograph (GC). High-speed imaging was conducted to illustrate the flame development. A single-zone model was used to evaluate the reactivity of LTR products. The GC measurements indicate that PRF0 and PRF50 cannot chemically react at low reformer temperature of 423 K. When the reformer temperature rises up to 523 K, LTR products mainly include hydrogen, carbon monoxides, aldehydes, alcohols, ketones, alkanes, olefins and alkynes. Due to the higher fuel reactivity, PRF0 produces more reformates than PRF50. According to the experimental engine analysis, the ignition timing is retarded significantly via LTR for both PRFs. The ignition timing difference of PRF0 due to LTR is larger than PRF50. The high-speed images reveal that LTR can lead to a slower flame development. Soot formation persists because of in-cylinder inhomogeneities, and can be lowered by LTR. The reactivity evaluation using the chemical modeling approach manifests that for PRF0 most of the LTR products inhibit mixture reactivity, while there is a large increase in the species enhancing reactivity for PRF50. The impacts of LTR products on ignition depend on both the chemical structure and the concentration in the mixture. The concentration of individual LTR product usually changes along with the reforming conditions. Thus LTR has the potential to control autoignition flexibly in HCCI engines.
A key challenge for the practical introduction of dual-fuel reactivity controlled compression ignition (RCCI) combustion modes in diesel engines is the requirement to store two fuels on-board. This work demonstrates that partially reforming diesel fuel into less reactive products is a promising method to allow RCCI to be implemented with a single stored fuel. Experiments were conducted using a thermally integrated reforming reactor in a reformed exhaust gas recirculation (R-EGR) configuration to achieve RCCI combustion using a light-duty diesel engine. The engine was operated at a low engine load and two reformed fuel percentages over ranges of exhaust gas recirculation (EGR) rate and main diesel fuel injection timing. Results show that RCCI-like emissions of NOx and soot were achieved load using the R-EGR configuration. It was also shown that complete fuel conversion in the reforming reactor is not necessary to achieve sufficiently low fuel reactivity for RCCI combustion. Overall engine brake thermal efficiency (BTE) was found to be slightly lower than for conventional diesel combustion (CDC) at the same overall fueling rate; however, increasing fumigant energy fraction (FEF) was shown to improve BTE. The presented data illustrated that further system optimization could allow R-EGR-based RCCI combustion systems to achieve BTE parity with CDC operation while maintaining extremely low engine-out soot and NOX emissions.
Advancements in catalytic reforming have demonstrated the ability to generate syngas (a mixture of CO and hydrogen) from a single hydrocarbon stream. This syngas mixture can then be used to replace diesel fuel and enable dual-fuel combustion strategies. The role of port-fuel injected syngas, comprised of equal parts hydrogen and carbon monoxide by volume was investigated experimentally for soot reduction benefits under a transient load change at constant speed. The syngas used for the experiments was presumed to be formed via a partial oxidation on-board fuel reforming process and delivered through gaseous injectors using a custom gas rail supplied with bottle gas, mounted in the swirl runner of the intake manifold. Time-based ramping of the direct-injected fuel with constant syngas fuel mass delivery from 2 to 8 bar brake mean effective pressure was performed on a multi-cylinder, turbocharged, light-duty engine to determine the effects of syngas on transient soot emissions. A Cambustion fNOx400 high-speed emissions analyzer and an AVL 439 opacimeter were used to quantify emissions under the load change to provide sub-cycle and cycle resolved resolution, respectively. Results show substantial soot reduction benefits with modest levels of syngas without significant increases in NOx emissions under the chosen conditions.
In-cylinder thermochemical fuel reforming (TFR), which involves running one cylinder rich of stoichiometric and routing its entire exhaust back into the intake manifold, is an attractive method for improving engine performances. Compared with other hydrocarbon fuels, the chemical structure of methane is more stable owing to much shorter carbon chain. As ethanol contains hydroxyl in chemical structure, it potentially generates OH radical during the combustion. Therefore, adding ethanol into natural gas (NG) might help the thermochemical reforming process in engine cylinder. This paper focused on researching the effects of ethanol-NG combined in-cylinder TFR on engine performances, before which the effect of NG in-cylinder TFR was examined in detail. Cylinder #4 (TFR cylinder) was running rich and its cooled exhaust was coupled to the intake manifold of a four-cylinder engine during the experiments. For NG in-cylinder TFR, a rapid decrease of brake specific fuel consumption was found when equivalence ratio of TFR cylinder reached about 1.2-1.3, at which substantial fraction of H2 and CO were confirmed in the reformed gas, under low load. However, compared with the case without TFR, global engine operation stability was worsened and distinct IMEP discrepancy between cylinder #2 (typical of cylinder #1, 2, 3) and TFR cylinder was resulted. For ethanol-NG combined in-cylinder TFR, results proved higher H2 and CO concentration in reformed gas and comparable fuel economy compared with NG in-cylinder TFR. Besides, more stable engine operation and lower NOx emission as well as smaller IMEP discrepancy between cylinder #2 and TFR cylinder was obtained.
Improvement of thermal efficiency is an important problem for internal combustion engines. Fuel reforming with dehydrogenation reaction by exhaust heat is one of the measures to increase thermal efficiency using hydrogen mixed SI combustion. For this kind engine system, hydrous ethanol has a good potential. Furthermore, when the hydrous ethanol inject to combustion chamber directory, high compression combustion can be achieved by its large amount of latent heat. Therefore, fuel lubricity is an important check point for the hydrous ethanol reforming engine systems. In this study, effect of water concentrations within ethanol on the hydrous ethanol fuel lubricity has been evaluated using HFRR (High-Frequency Reciprocating Rig) test method. Wear scar diameter on 100 % of ethanol was around 700 μm which was a little better than gasoline lubricity. When the water concentration within ethanol was increased, the wear scar diameters were decreasing around 330 μm. Considering this phenomenon by the fuel viscosity, the viscosity of hydrous ethanol is growing with increasing water concentration up to 50-60 %. It seems that lubricity of hydrous ethanol can be kept by fluid film lubrication mode up to 50-60 % of water concentration.
Negative Valve Overlap (NVO) is a potential control strategy for enabling Low-Temperature Gasoline Combustion (LTGC) at low loads. While the thermal effects of NVO fueling on main combustion are well-understood, the chemical effects of NVO in-cylinder fuel reforming have not been extensively studied. The objective of this work is to examine the effects of fuel molecular structure on NVO fuel reforming using gas sampling and detailed speciation by gas chromatography. Engine gas samples were collected from a single-cylinder research engine at the end of the NVO period using a custom dump-valve apparatus. Six fuel components were studied at two injection timings: (1) iso-octane, (2) n-heptane, (3) ethanol, (4) 1-hexene, (5) cyclohexane, and (6) toluene. All fuel components were studied neat except for toluene - toluene was blended with 18.9% nheptane by liquid volume to increase the fuel reactivity. Additionally, a gasoline surrogate matching the broad molecular composition of RD587 gasoline was formulated using the chosen fuel palette and tested. The energy content of the injected fuel mass was kept constant for the sampled NVO cycle and the excess oxygen was relatively low (2.4%) compared to previous studies by the authors. The later injection timing studied resulted in useable recovered fuel energy near 70% and improved reformate yield of hydrogen and C1-C4 hydrocarbons compared to the earlier injection timing for all fuels except toluene/n-heptane. Analysis of the RD587 surrogate reformate compared to the individual component reformates suggests that fuel component interactions depend on injection timing, potentially through the in-cylinder equivalence ratio distribution.
Gasoline direct injection (GDI) engines have become very attractive in transportation due to several benefits over preceding engine technologies. However, GDI engines are associated with higher levels of particulate matter (PM) emissions, which is a major concern for human health. The aim of this work is to broaden the understanding of the effect of hydrogen combustion and the influence of the three way catalytic converter (TWC) on PM emission characteristics. The presence of hydrogen in GDI engines has been reported to reduce fuel consumption and improve the combustion process, making it possible to induce higher rates of EGR. A prototype exhaust fuel reformer build for on-board vehicle hydrogen-rich gas (reformate) production has been integrated within the engine operation and studied in this work. It is concluded that benefits on engine out soot emissions from the combustion of the reformate-gas are more noticeable in the engine operation conditions with a higher concentration of soot particulates.
A fuel reformer system that uses a steam reforming reaction in the exhaust gas recirculation (EGR) line with a catalyst was earlier proposed.(1) An analysis of engine test results revealed that not only hydrogen (H2) but also a H2 rich reformate additive in the air-fuel mixture was effective in suppressing knocking. To improve fuel economy via a high compression ratio, the knock limit is extended through the addition of H2 with its high octane number. In order to produce H2 on-board, we have proposed a fuel reformer for which the additions to the engine are an injector and a catalyst in the existing cooled EGR system. This method produces thicker H2 gas from gasoline by using heat and water vapor in the exhaust gas. The reformate mainly consists of H2, CO and CH4. The results of a previous study showed that hydrogen's high-speed flame had the effect of extending the EGR limit and that the reformate components besides hydrogen did not inhibit this effect.(1) Because the fuel has a higher octane number than ordinary gasoline, it is hypothesized that adding the reformate to the gasoline mixture might not only extend the EGR limit but also have an anti-knocking effect. In the present study, it was confirmed that RON of the total fuel in the engine was improved by around 2% by the reformate additive in this fuel reformer system. CO contained in the reformate gas had a negligible effect on eliminating H2's anti-knocking effect and the reformate gas additive can improve engine torque and fuel consumption like pure H2 under an operating condition with noticeable knocking. Finally, indicated specific fuel consumption was reduced by 1.6% as the anti-knocking effect of reformate H2 extended the knock limit by 6 degrees.
On-board hydrogen generation technology using a fuel reforming catalyst is an effective way to improve the fuel efficiency of automotive internal combustion engines. The main issue to be addressed in developing such a catalyst is to suppress catalyst deterioration caused by carbon deposition on the catalyst surface due to sulfur adsorption. Enhancing the hydrocarbon and water activation capabilities of the catalyst is important in improving catalyst durability. It was found that the use of a rare earth element is effective in improving the water activation capability of the catalyst. Controlling the hydrocarbon activation capability of the catalyst for a good balance with water activation was also found to be effective in improving catalyst durability.
Negative valve overlap (NVO) is a viable control strategy that enables low-temperature gasoline combustion (LTGC) at low loads. Thermal effects of NVO fueling on main combustion are well understood, but fuel reforming chemistry during NVO has not been extensively studied. The objective of this work is to analyze the impact of global equivalence ratio and available oxidizer on NVO product concentrations. Experiments were performed in a LTGC single-cylinder engine under a sweep of NVO oxygen concentration and NVO fueling rates. Gas sampling at the start and end of the NVO period was performed via a custom dump-valve apparatus with detailed sample speciation by gas chromatography. Single-zone reactor models using detailed chemistry at relevant mixing and thermodynamic conditions were used in parallel to the experiments to evaluate expected yields of partially oxidized species under representative engine time scales. Modeling efforts help identify physical mechanisms that further describe experimental findings with regards to anticipated fuel-fraction and temperature fields. For the NVO fueling sweep, end-cycle CO2 concentrations remained essentially flat, while intermediate species concentrations rose as fueling rates increased. The rate-of-increase was most pronounced for the C3-C4 hydrocarbons whose rate-of-increase was greater than the relative increase in fueling rate. Modeling results suggest that oxygen depleted environments coupled with lower heat release temperatures result in slower reforming rates, which yielded higher C3-C4 production. For the oxygen concentration sweep with fixed NVO fueling, CO and CO2 products increased as the amount of oxidizer likewise increased. These increases came at the expense of intermediate hydrocarbon yields.
In light of the increasingly stringent efficiency and emissions requirements, several new engine technologies are currently under investigation. One of these new concepts is the Dedicated EGR (D-EGR®) engine. The concept utilizes fuel reforming and high levels of recirculated exhaust gas (EGR) to achieve very high levels of thermal efficiency. While the positive impact of reformate, in particular hydrogen, on gasoline engine performance has been widely documented, the on-board reforming process and / or storage of H2 remains challenging. The Water-Gas-Shift (WGS) reaction is well known and has been used successfully for many years in the industry to produce hydrogen from the reactants water vapor and carbon monoxide. For this study, prototype WGS catalysts were installed in the exhaust tract of the dedicated cylinder of a turbocharged 2.0 L in-line four cylinder MPI engine. The potential of increased H2 production in a D-EGR engine was evaluated through the use of these catalysts. Furthermore, the impact on engine performance was also examined. By using a WGS catalyst, H2 levels can be increased significantly, leading to further improved burn durations, combustion instabilities, decreased HC emissions, and greater knock resistance which can directly translate into enhanced engine efficiency. In addition, this paper also briefly discusses the current shortcomings of the WGS technology in an engine environment.
To improve the fuel economy via high EGR, combustion stability is enhanced through the addition of hydrogen, with its high flame-speed in air-fuel mixture. So, in order to realize on-board hydrogen production we developed a fuel reformer which produces hydrogen rich gas. One of the main issues of the reformer engine is the effects of reformate gas components on combustion performance. To clarify the effect of reformate gas contents on combustion stability, chemical kinetic simulations and single-cylinder engine test, in which hydrogen, CO, methane and simulated gas were added to intake air, were executed. And it is confirmed that hydrogen additive rate is dominant on high EGR combustion. The other issue to realize the fuel reformer was the catalyst deterioration. Catalyst reforming and exposure test were carried out to understand the influence of actual exhaust gas on the catalyst performance. Fresh catalyst showed good performance in generating hydrogen, but an aged catalyst generated only half as compared to a fresh catalyst. So we considered measures to improve catalyst performance. According to EGR reforming performance test with single-cylinder engine using conventional catalyst and an improved catalyst, the improved catalyst showed good performance. Finally, in order to confirm the performance of hydrogen generation and the effects of real reformate gas on EGR combustion, a single-cylinder engine with the fuel reformer was developed. It is confirmed that hydrogen is generated from gasoline and EGR gas by the fuel reformer, and combustion stability under high EGR rate is enhanced by reformate hydrogen.
To explore the exergy loss of engine combustion process, entropy generations were numerically analyzed through detailed chemical kinetics. It revealed that the reformed fuel with simpler molecular tended to produce lower combustion irreversibility. Furthermore, a promising high efficiency RM- HCCI (Reformed molecule HCCI) combustion principle was proposed. In a RM-HCCI engine, hydrocarbon fuels were reformed into small molecule fuels under high temperature and low/no oxygen atmosphere before injection into the cylinder when the exhaust gas enthalpy to a certain extent was recovered, further improving the engine efficiency. The second law efficiency (η2nd) of a RM-HCCI combustion with a CR of 10 can be increased from 36.78% to 45.47% by coordination of multiple control parameters, and to 67.79% by raising CR from 10 to 100. The RM-HCCI has many advantages: (1) less exergy losses during combustion processes, (2) longer ignition delays and shorter but controlled combustion durations, (3) improved ratio of specific heats, all these advantages can improve engine efficiency.
Southwest Research Institute (SwRI) converted a 2012 Buick Regal GS to use an engine with Dedicated EGR™ (D-EGR™). D-EGR is an engine concept that uses fuel reforming and high levels of recirculated exhaust gas (EGR) to achieve very high levels of thermal efficiency [1]. To accomplish reformation of the gasoline in a cost-effective, energy efficient manner, a dedicated cylinder is used for both the production of EGR and reformate. By operating the engine in this manner, many of the sources of losses from traditional reforming technology are eliminated and the engine can take full advantage of the benefits of reformate. The engine in the vehicle was modified to add the following components: the dedicated EGR loop, an additional injector for delivering extra fuel for reformation, a modified boost system that included a supercharger, high energy dual coil offset (DCO) ignition and other actuators used to enable the control of D-EGR combustion. In addition, the compression ratio of the engine was increased to 11.7:1 to take advantage of the improved knock resistance from reformate and EGR. The engine conversion and the development of the control system for the engine are the subject of this paper. The conversion to D-EGR configuration resulted in an improvement in engine efficiency of at least 10% across the performance map, with some operating conditions seeing substantially higher improvements. For example, the brake specific fuel consumption (BSFC) at 2000 rpm 2 bar BMEP improved from 385 g/kW-h in the series production state to 330 g/kW-h and the lowest BSFC for the engine was 212 g/kWh compared to 236 g/kW-h for the series engine. The addition of 2-stage boosting also allowed the engine to meet its torque targets of at least 17 bar BMEP from 1500-5500 rpm while maintaining good transient response and low engine-out emissions.
The regulations for mobile applications will become stricter in Euro 6 and further emission levels and require the use of active aftertreatment methods for NOX and particulate matter. SCR and LNT have been both used commercially for mobile NOX removal. An alternative system is based on the combination of these two technologies. Developments of catalysts and whole systems as well as final vehicle demonstrations are discussed in this study. The small and full-size catalyst development experiments resulted in PtRh/LNT with optimized noble metal loadings and Cu-SCR catalyst having a high durability and ammonia adsorption capacity. For this study, an aftertreatment system consisting of LNT plus exhaust bypass, passive SCR and engine independent reductant supply by on-board exhaust fuel reforming was developed and investigated. The concept definition considers NOX conversion, CO2 drawback and system complexity. The passive SCR significantly contributes to the total NOX conversion over a broad temperature range. In contrary to conventional LNT applications, the LNT NOX slip does not directly reduce the system NOX conversion but can be converted over the passive SCR. Thereby, the NOX adsorption duration might be prolonged, resulting in lower LNT regeneration frequency and less fuel consumption, resp. CO2 emissions. Additionally, the engine independent LNT enrichment is beneficial regarding fuel consumption in comparison to conventional engine internal enrichment. The system has been tested in a vehicle in combination with a highly efficient Diesel engine. Results regarding CO2 and NOX as well as their dependency on temperatures are shown here.
Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) and other forms of advanced combustion. When fuel is injected into O2-deficient NVO conditions, a portion of the fuel can be converted to products containing significant levels of H2 and CO. Additionally, other short chain hydrocarbons are produced by means of thermal cracking, water-gas shift, and partial oxidation reactions. The present study experimentally investigates the fuel reforming chemistry that occurs during NVO. To this end, two very different experimental facilities are utilized and their results are compared. One facility is located at Oak Ridge National Laboratory, which uses a custom research engine cycle developed to isolate the NVO event from main combustion, allowing a steady stream of NVO reformate to be exhausted from the engine and chemically analyzed. The other experimental facility, located at Sandia National Laboratories, uses a dump valve to capture the exhaust from a single NVO event for analysis. Results from the two experiments are in excellent trend-wise agreement and indicate that the reforming process under low-O2 conditions produces substantial concentrations of H2, CO, methane, and other short-chain hydrocarbon species. The concentration of these species is found to be strongly dependent on fuel injection timing and injected fuel type, with weaker dependencies on NVO duration and initial temperature, indicating that NVO reforming is kinetically limited. Further, NVO reforming does not require a large energy input from the engine, meaning that it is not thermodynamically expensive. The implications of these results on HCCI and other forms of combustion are discussed in detail.
Exhaust Gas Fuel Reforming has potential to be used for on-board generation of hydrogen rich gas, reformate, and to act as an energy recovery system allowing the capture of waste exhaust heat. High exhaust gas temperature drives endothermic reforming reactions that convert hydrocarbon fuel into gaseous fuel when combined with exhaust gas over a catalyst - the result is an increase in overall fuel energy that is proportional to waste energy capture. The paper demonstrates how the combustion of reformate in a direct injection gasoline (GDI) engine via Reformed Exhaust Gas Recirculation (REGR) can be beneficial to engine performance and emissions. Bottled reformate was inducted into a single cylinder GDI engine at a range of engine loads to compare REGR to conventional EGR. The reformate composition was selected to approximate reformate produced by exhaust gas fuel reforming at typical gasoline engine exhaust temperatures. The decision was guided by data from experimental work carried out by Johnson Matthey using a reforming catalyst developed for the fuel reforming application. The engine test results show improved combustion stability with REGR; this allows for higher recirculation rates and increased combustion mixture dilution. This is significant as it could allow for a higher fraction of fuel to be reformed, and therefore waste energy captured. REGR results in a large NOx reduction and a reduction in HCs relative to EGR. The effects of REGR on Particulate Matter (PM) emissions were also analysed, concluding that REGR reduces PM mass compared to conventional EGR.
A study on the overall performance of an engine powered with hydrogen-enriched NG at stoichiometric condition, for different hydrogen shares have been described in this paper. The research has been carried on a General Motors Company X16SZR 4-cylinder, 4-stroke 1600 cm3 engine. Engine dynamometer tests were complemented with mathematical model calculations. Tested engine has been equipped with an aftermarket CNG feeding system where fuel is being injected into intake manifold simultaneously under low overpressure. Research program provided analysis for fuel blends with variable methane/hydrogen volume proportion (%): 100/0, 95/5, 90/10, 85/15, 80/20, 70/30, 60/40 and 50/50. Ignition timing and all other strategies, excluding EGR, remained unvaried. Testing procedure provided three different steady-state engine operation points for each of 8 different fuels: idle, high speed without load and full power at speeds in range of 1500-3500 rpm. The main aspect of the analysis was to identify the influence of hydrogen share on engine parameters such power, fuel consumption, in-cylinder pressure, temperature and exhaust gas composition. Very significant possibility of CO₂ emission reduction has been identified. Authors do also attempt to identify optimal blend for applications without any significant changes into engine construction and ignition/timing calibration. All possible negative effects of increasing hydrogen share have also been taken into consideration - like knocking. Analysis carried out on the basis of results allowed it to the point on methane/hydrogen proportion in fuel blend considering a total efficiency, emission and heat flux in parts of combustion chamber in engine. The results provide a basis for further studies on optimization of the process of managing the process of combustion in car engines fuelled by CNG and equipped with fuel reformer or using natural gas and hydrogen mixtures prepared at a filling station.
Items per page:
50
1 – 50 of 165