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

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

A highly efficient six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery

A concept adding two strokes to the Otto or Diesel engine cycle to increase fuel efficiency is presented here. It can be thought of as a four-stroke Otto or Diesel cycle followed by a two-stroke heat recovery steam cycle. A partial exhaust event coupled with water injection adds an additional power stroke. Waste heat from two sources is effectively converted into usable work: engine coolant and exhaust gas. An ideal thermodynamics model of the exhaust gas compression, water injection and expansion was used to investigate this modification. By changing the exhaust valve closing timing during the exhaust stroke, the optimum amount of exhaust can be recompressed, maximizing the net mean effective pressure of the steam expansion stroke (MEP_steam). The valve closing timing for maximum MEP_steam is limited by either 1 bar or the dew point temperature of the expansion gas/moisture mixture when the exhaust valve opens. The range of MEP_steam calculated for the geometry of a conventional gasoline engine and is from 0.75 to 2.5 bars. Typical combustion mean effective pressures (MEP_combustion) of naturally aspirated gasoline engines are up to 10 bar, thus this concept has the potential to significantly increase the engine efficiency and fuel economy.     

高/低压EGR对汽油机和增压器影响的试验研究

在一款涡轮增压汽油缸内直喷(gasoline direct injection,GDI)汽油机上进行了高压(HP)废气再循环(exhaust gas recirculation,EGR)和低压(LP)EGR对发动机和增压器性能影响的试验研究。分别对比了HP EGR和LP EGR系统在外特性和部分负荷工况对发动机燃烧、油耗、进排气的影响及增压器相应的工况变化,并分析了出现这些变化的原因。结果表明,汽油机EGR系统能够优化缸内燃烧,减少泵气损失,从而降低油耗。低压EGR系统在部分负荷工况热效率比高压EGR更高,主要原因为低压EGR系统的涡轮增压器可利用的尾气能量更多,且进入发动机的废气温度较低,能进一步优化缸内燃烧。     

Application of exhaust gas fuel reforming in diesel and homogeneous charge compression ignition (HCCI) engines fuelled with biofuels

This paper documents the application of exhaust gas fuel reforming of two alternative fuels, biodiesel and bioethanol, in internal combustion engines. The exhaust gas fuel reforming process is a method of on-board production of hydrogen-rich gas by catalytic reaction of fuel and engine exhaust gas. The benefits of exhaust gas fuel reforming have been demonstrated by adding simulated reformed gas to a diesel engine fuelled by a mixture of 50% ultra low sulphur diesel (ULSD) and 50% rapeseed methyl ester (RME) as well as to a homogeneous charge compression ignition (HCCI) engine fuelled by bioethanol. In the case of the biodiesel fuelled engine, a reduction of NO_x emissions was achieved without considerable smoke increase. In the case of the bioethanol fuelled HCCI engine, the engine tolerance to exhaust gas recirculation (EGR) was extended and hence the typically high pressure rise rates of HCCI engines, associated with intense combustion noise, were reduced.     

Influence of methanol reformate injection strategy on performance,available exhaust gas enthalpy and emissions of a direct-injection spark ignition engine

This paper presents experimental study results of a direct injection engine fed with methanol steam reforming products and devised to work with a high-pressure thermochemical recuperation system. The influence of injection pressure and timing on heat release rate, fuel mass fraction burned, cycle-to-cycle variation, pollutant emissions, efficiency and exhaust gas energy available for methanol reforming is investigated and analyzed. Effect of injector flow area on the required injection pressure is discussed. End-of-injection (EOI) timing is shown to be the main influencing factor on engine efficiency and pollutant emissions. The obtained results indicate that there is a range of EOI timing where indicated efficiency is almost constant and NO_x emissions drop by a factor of 2.5. Particle number emissions can be reduced in this range by a factor of 4. We showed that engine exhaust gas possesses enough energy to sustain endothermic reforming reactions up to excess air ratio of 2.5.     

The effects of hydrogen on the combustion,performance and emissions of a turbo gasoline direct-injection engine with exhaust gas recirculation

The effects of hydrogen on the combustion characteristics, thermal efficiency, and emissions of a turbo gasoline direct-injection engine with exhaust gas recirculation (EGR) were investigated experimentally at brake mean effective pressures of 4, 6, and 8 bar at 2000 rpm. Four cases of hydrogen energy fraction (0%, 1%, 3% and 5%) of total fuel energy were studied. Hydrogen energy fraction of total fuel energy was hydrogen energy in the sum of energy of consumed gasoline and added hydrogen. The test results demonstrated that hydrogen addition improved the combustion speed and reduced cycle-to-cycle variation. In particular, cylinder-to-cylinder variation dramatically decreased with hydrogen addition at high EGR rates. This suggests that the operable EGR rate can be widened for a turbo gasoline direct-injection engine. The improved combustion and wider operable EGR rate resulted in enhanced thermal efficiency. However, the turbocharging effect acted in opposition to the thermal efficiency with respect to the EGR rate. Therefore, a different strategy to improve the thermal efficiency with EGR was required for the turbo gasoline direct-injection engine. HC and CO₂ emissions were reduced but NO_X emissions increased with hydrogen addition. The CO emissions as a function of engine load followed different trends that depended on the level of hydrogen addition.     

Comparative engine performance and emission analysis of CNG and gasoline in a retrofitted car engine

A comparative analysis is being performed of the engine performance and exhaust emission on a gasoline and compressed natural gas (CNG) fueled retrofitted spark ignition car engine. A new 1.6 L, 4-cylinder petrol engine was converted to the computer incorporated bi-fuel system which operated with either gasoline or CNG using an electronically controlled solenoid actuated valve mechanism. The engine brake power, brake specific fuel consumption, brake thermal efficiency, exhaust gas temperature and exhaust emissions (unburnt hydrocarbon, carbon mono-oxide, oxygen and carbon dioxides) were measured over a range of speed variations at 50% and 80% throttle positions through a computer based data acquisition and control system. Comparative analysis of the experimental results showed 19.25% and 10.86% reduction in brake power and 15.96% and 14.68% reduction in brake specific fuel consumption (BSFC) at 50% and 80% throttle positions respectively while the engine was fueled with CNG compared to that with the gasoline. Whereas, the retrofitted engine produced 1.6% higher brake thermal efficiency and 24.21% higher exhaust gas temperature at 80% throttle had produced an average of 40.84% higher NO_x emission over the speed range of 1500–5500 rpm at 80% throttle. Other emission contents (unburnt HC, CO, O₂ and CO₂) were significantly lower than those of the gasoline emissions.     

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

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

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

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

Comparison and Selection Research of CO2-Based Transcritical Rankine Cycle Using for Gasoline and Diesel Engine's Waste Heat Recovery

This paper presents a theoretical study of CO₂-based transcritical Rankine cycle (CTRC) for engine's waste heat recovery, involving comparison and selection of four CTRC configurations for two engine types, namely a gasoline engine and a diesel engine. The results of configuration comparison show that the CTRC configuration with both a preheater and a regenerator may be more suitable for both two type engines with water-cooling system. If only recovering the waste heat of exhaust gas, the regenerated CTRC configuration may be more appropriate. The results of engine type comparison show that engine load has slighter effect on the CTRC performance for the gasoline engine compared with that for the diesel engine. Particularly, this paper jointly considers the effect of CTRC weight to evaluate the final CTRC output, which is significant for the vehicle engine. A critical weight is found for the two engines based on 100% engine load, 215 kg for the gasoline engine and 998 kg for the diesel engine, which is the upper limitation of the CTRC weight design. When considering the weight effect, the diesel engine may be the more suitable recovery target compared with the gasoline engine, owing to the more stable reaction of output performance to the CTRC weight.     

Reduction of fuel consumption in gasoline engines by introducing HHO gas into intake manifold

Brown’s gas (HHO) has recently been introduced to the auto industry as a new source of energy. The present work proposes the design of a new device attached to the engine to integrate an HHO production system with the gasoline engine. The proposed HHO generating device is compact and can be installed in the engine compartment. This auxiliary device was designed, constructed, integrated and tested on a gasoline engine.     

Effect of heat exchanger material and fouling on thermoelectric exhaust heat recovery

Thermoelectric devices are being investigated as a means of improving fuel economy for diesel and gasoline vehicles through the conversion of wasted fuel energy, in the form of heat, to useable electricity. By capturing a small portion of the energy that is available with thermoelectric devices can reduce engine loads thus decreasing pollutant emissions, fuel consumption, and CO₂ to further reduce green house gas emissions. This study is conducted in an effort to better understand and improve the performance of thermoelectric heat recovery systems for automotive use. For this purpose an experimental investigation of thermoelectrics in contact with clean and fouled heat exchangers of different materials is performed. The thermoelectric devices are tested on a bench-scale thermoelectric heat recovery apparatus that simulates automotive exhaust. It is observed that for higher exhaust gas flowrates, thermoelectric power output increases from 2 to 3.8 W while overall system efficiency decreases from 0.95% to 0.6%. Degradation of the effectiveness of the EGR-type heat exchangers over a period of driving is also simulated by exposing the heat exchangers to diesel engine exhaust under thermophoretic conditions to form a deposit layer. For the fouled EGR-type heat exchangers, power output and system efficiency is observed to be 5-10% lower for all conditions tested.     

Theoretical study on the effect of low-temperature reforming on gasoline compression ignition (GCI) at low-load conditions

In this paper, the influence of reforming conditions on the reforming products of gasoline, as well as the effect of main reforming products on GCI combustion at low-load conditions has been studied by experiment and numerical simulation. The results show CO, H₂ and CH₄ are the major reforming products, and their production is improved by higher reforming temperature, oxygen concentration and reforming time. The production of CO and H₂ is mainly determined by the dehydrogenation reaction between fuel molecules and OH, while the one between iC₈H₁₈ and O₂ is essential for the CH₄ generation. The combustion efficiency rises sharply with more CO addition, but increases first and then decreases with increased H₂, while the peak value of 96.71% is achieved. Besides, higher combustion efficiency is obtained with more internal exhaust gas recirculation (i-EGR) used. The increased OH and H radicals can be attained by adding CH₄, which further improves combustion efficiency.     

A numerical study on methanol steam reforming reactor utilizing engine exhaust heat for hydrogen generation

Internal combustion engines are used in most vehicles around the world to power the transport sector. Efficiency improvement, emission reduction, and utilization of alternative fuels are the main aspects of current IC engine research. Hydrogen-enhanced combustion proved to be one of the efficient ways to achieve such goals. But the problem lies in the storage of hydrogen for the transportation sector, and on-board fuel reforming is a promising option for solving this issue. It deals with transforming a suitable liquid fuel (methanol) into an H₂-rich gas using a catalytic conversion process. For sustaining the reforming reaction, the required heat energy is taken from engine exhaust waste heat, this process is known as thermochemical recuperation. Number of studies on the reformers utilized for on-board hydrogen generation using engine exhaust heat are limited in the literature. The present study investigates the performance of a reactor that uses the exhaust gas heat energy for sustaining the reforming reaction. A numerical analysis was performed over a selected reactor where exhaust gases were flowing at one side, while on the other, the reforming reaction was taking place with the help of heat provided by high-temperature exhaust gases. A packed bed-type reactor was chosen for the current study and a parametric study was conducted where the effects of various operating parameters on both reacting and heating sides on the reactor's performance were investigated. It was found that temperature was the most influential inlet parameter among others. Steam/Carbon ratio and flow configuration had a negligible effect on the hydrogen yield as well as methanol conversion. Reactant inlet velocity increment revealed a significant drop in methanol conversion as it reduces the residence time for reforming reaction in the catalyst zone.     

Modeling and simulation of hydrogen production from dimethyl ether steam reforming using exhaust gas

In this paper, hydrogen production from steam reforming of DME (dimethyl ether) has been modeled and simulated using a CFD (computational fluid dynamics) method. The reformation chemistry occurs in a porous catalytic bed where exhaust gas is supplied through the EGR (exhaust gas recycling) valve of the engine to drive the endothermic reaction system. The tightly coupled system of mass, energy, and momentum equations are used to describe the complex physical and chemical process of DME steam reforming. The global reaction kinetics for the reforming is adopted in the CFD model. The mathematical models are introduced into the commercial software Comsol, and then numerical simulations are also performed based on this model. The model predictions are quantitatively validated by experiment data. The simulation results indicate the temperature distribution, mass distribution, DME conversion, and hydrogen production from steam reforming of DME. In addition, the fuel to steam ratio and velocity of exhaust gas are manipulated as operating parameters. These simulation results will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor. Copyright © 2015 John Wiley & Sons, Ltd.     

Emission components characteristics of a bi-fuel vehicle at idling condition

Natural gas (NG) represents today a promising alternative to conventional fuels for road vehicles propulsion, since it is characterized by a relatively low cost, better geopolitical distribution than oil, and lower environmental impact. This explains the current spreading of compressed natural gas (CNG) fuelled spark ignition (SI) engine, above all in the bi-fuel version, which is able to run either with gasoline or with NG. However, the aim of the present investigation is to evaluate the emission characteristics at idling condition. The vehicle engine was converted to bi-fueling system from a gasoline engine, and operated separately either with gasoline or CNG. Two different fuel injection systems (i.e., multi-point injection (MPI)-sequential and closed-loop venturi-continuous) are used, and their influences on the formation of emissions at different operating conditions are examined. A detailed comparative analysis of the engine exhaust emissions using gasoline and CNG is made. The results indicate that the CNG shows low air index and lower emissions of carbon monoxide (CO), carbon dioxide (CO₂), and total hydrocarbon (THC) compared to gasoline.     

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 (R_EG) 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 R_EG 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 R_EG of 6%.     

Production of dimethyl ether and hydrogen by methanol reforming for an HCCI engine system with waste heat recovery – Continuous control of fuel ignitability and utilization of exhaust gas heat

Homogeneous charge compression ignition (HCCI) is a promising technique to achieve high thermal efficiency and clean exhaust with internal combustion engines. However, the difficulty in ensuring optimal ignition timing control prevents its practical application. Previous research has shown that adjusting the proportion of dimethyl ether (DME) and hydrogen-containing methanol-reformed gas (MRG) can control the ignition timing in an HCCI combustion engine fueled with the two fuels. As both DME and MRG can be produced in endothermic methanol reforming reactions, onboard reforming utilizing the exhaust gas heat can recover the waste heat from the engine. A very high overall thermal efficiency can be achieved by combining the high engine efficiency with HCCI and the waste heat recovery. This research investigates the basic characteristics of methanol reforming in a reactor tube with different catalysts with the aim to produce fuels for the HCCI combustion system.     

Theoretical Investigation of Waste Heat Recovery from an IC Engine Using Vapor Absorption Refrigeration System and Thermoelectric Converter

This study proposes the preliminary simulation of a single cylinder spark ignition engine with waste heat recovery system. To harvest waste heat energy from the engine exhaust a thermoelectric generator coupled to a vapor absorption refrigeration (VAR) system was proposed in this simulation work. Parametric simulation of engine, thermoelectric generator and VAR using thermodynamic relations was carried out in MATLAB – Simulink software. An attempt has been made mathematically to integrate engine, thermoelectric generator and VAR system to study the effect of engine load, speed, equivalence ratio on thermoelectric output and coefficient of performance (COP) of a VAR system. In this study, the VAR system runs by taking heat energy from the exhaust gas and the electric power produced by a thermoelectric generator was utilized to run the pump of the refrigeration system. It was found that COP of the absorption refrigeration system depends on engine load, speed and air fuel equivalence ratio. The study also reveals that about 10% to 15% of the total exhaust energy can be harvested using this system.     

HCCI甲醇发动机的燃烧与排放特性

在Ricardo Hydra单缸四冲程发动机上利用内部废气再循环策略实现了甲醇燃料的HCCI燃烧.通过调整HCCI发动机的过量空气系数和转速,研究了HCCI甲醇发动机的燃烧和排放特性.结果表明,甲醇燃料的HCCI燃烧不同于普通汽油,其着火更早、燃烧更快,但在低转速时,平均指示压力相对较低.甲醇燃料可以在更稀的混合气条件下实现HCCI燃烧.在相同的转速和过量空气系数下,甲醇燃料的NOx和HC排放低于汽油.