Effect of hydroxy (HHO) gas addition on performance and exhaust emissions in compression ignition engines

In this study, hydroxy gas (HHO) was produced by the electrolysis process of different electrolytes (KOH_(aq), NaOH_(aq), NaCl_(aq)) with various electrode designs in a leak proof plexiglass reactor (hydrogen generator). Hydroxy gas was used as a supplementary fuel in a four cylinder, four stroke, compression ignition (CI) engine without any modification and without need for storage tanks. Its effects on exhaust emissions and engine performance characteristics were investigated. Experiments showed that constant HHO flow rate at low engine speeds (under the critical speed of 1750 rpm for this experimental study), turned advantages of HHO system into disadvantages for engine torque, carbon monoxide (CO), hydrocarbon (HC) emissions and specific fuel consumption (SFC). Investigations demonstrated that HHO flow rate had to be diminished in relation to engine speed below 1750 rpm due to the long opening time of intake manifolds at low speeds. This caused excessive volume occupation of hydroxy in cylinders which prevented correct air to be taken into the combustion chambers and consequently, decreased volumetric efficiency was inevitable. Decreased volumetric efficiency influenced combustion efficiency which had negative effects on engine torque and exhaust emissions. Therefore, a hydroxy electronic control unit (HECU) was designed and manufactured to decrease HHO flow rate by decreasing voltage and current automatically by programming the data logger to compensate disadvantages of HHO gas on SFC, engine torque and exhaust emissions under engine speed of 1750 rpm. The flow rate of HHO gas was measured by using various amounts of KOH, NaOH, NaCl (catalysts). These catalysts were added into the water to diminish hydrogen and oxygen bonds and NaOH was specified as the most appropriate catalyst. It was observed that if the molality of NaOH in solution exceeded 1% by mass, electrical current supplied from the battery increased dramatically due to the too much reduction of electrical resistance. HHO system addition to the engine without any modification resulted in increasing engine torque output by an average of 19.1%, reducing CO emissions by an average of 13.5%, HC emissions by an average of 5% and SFC by an average of 14%.     

Hydrogen-fueled internal combustion engines

The threat posed by climate change and the striving for security of energy supply are issues high on the political agenda these days. Governments are putting strategic plans in motion to decrease primary energy use, take carbon out of fuels and facilitate modal shifts.     

Progress in high performance,low emissions,and exergy recovery in internal combustion engines

This article first gives a brief review of thermal engines designed for terrestrial transportation since the 1900s. We then outline the main developments in the state of the art and knowledge about internal combustion engines, focusing on the increasingly stringent pollution constraints imposed since the 1990s. The general concept of high‐energy performance machines is analyzed from the energy, exergy, and public health point of view and illustrated with typical examples of clean energy production and zero emissions. Whereas the energy analysis revealed high potential of waste heat recovery from both exhaust and cooling system, the exergetic analysis revealed much higher recovery potential from exhaust gases. The exergy content of exhaust gases was observed to be within the range from 10.4% to 20.2% of the fuel energy. The cooling exergy is within the range from 1.2% to 3.4% of the fuel energy. The article concludes with some perspectives for the emergence of an economic model that could be applied to land‐based transport systems in the framework of energy transition by 2030. Copyright © 2016 John Wiley & Sons, Ltd.     

Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines

The increasing industrialization and motorization of the world has led to a steep rise for the demand of petroleum-based fuels. Petroleum-based fuels are obtained from limited reserves. These finite reserves are highly concentrated in certain regions of the world. Therefore, those countries not having these resources are facing energy/foreign exchange crisis, mainly due to the import of crude petroleum. Hence, it is necessary to look for alternative fuels which can be produced from resources available locally within the country such as alcohol, biodiesel, vegetable oils etc. This paper reviews the production, characterization and current statuses of vegetable oil and biodiesel as well as the experimental research work carried out in various countries. This paper touches upon well-to-wheel greenhouse gas emissions, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, engine performance and emissions, effect on wear, lubricating oil etc.     

Analysis of the particulate emissions and combustion performance of a direct injection spark ignition engine using hydrogen and gasoline mixtures

Three different fractions (2%, 5%, and 10% of stoichiometric, or 2.38%, 5.92%, and 11.73% by energy fraction) of hydrogen were aspirated into a gasoline direct injection engine under two different load conditions. The base fuel was 65% iso-octane, and 35% toluene by volume fraction. Ignition sweeps were conducted for each operation point. The pressure traces were recorded for further analysis, and the particulate emission size distributions were measured using a Cambustion DMS500. The results indicated a more stable and faster combustion as more hydrogen was blended. Meanwhile, a substantial reduction in particulate emissions was found at the low load condition (more than 95% reduction either in terms of number concentration or mass concentration when blending 10% hydrogen). Some variation in the results occurred at the high load condition, but the particulate emissions were reduced in most cases, especially for nucleation mode particulate matter. Retarding the ignition timing generally reduced the particulate emissions. An engine model was constructed using the Ricardo WAVE package to assist in understanding the data. The simulation reported a higher residual gas fraction at low load, which explained the higher level of cycle-by-cycle variation at the low load.     

Influence of hydrogen enriched gas injection upon polluting emissions from pulverized coal combustion

This paper presents the experimental results on the pollutant emission of a 2 MW thermal pilot furnace with the injection of hydrogen enriched gas (HRG) into the primary jet (coal dust and primary air). An experimental method to study the effects of this procedure on the thermal pilot furnace, which was specially designed to burn pulverized solid fuel, was conducted. The hydrogen enriched gas used in the study is dried and was produced by an electrolytic system still under patent by the authors. The primary conclusions from the results are focused on the quick diffusion of hydrogen, unlike oxygen, within the coal particles and that the hydrogen forms stable compounds with the sulfur and other elements the sterile content. A primary chemical analysis of the ash/sludge components is also presented within the paper.     

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Burning hydrogen in conventional internal combustion (IC) engines is associated with zero carbon-based tailpipe exhaust emissions. In order to obtain high volumetric efficiency and eliminate abnormal combustion modes such as preignition and backfire, in-cylinder direct injection (DI) of hydrogen is considered preferable for a future generation of hydrogen IC engines. However, hydrogen's low density requires high injection pressures for fast hydrogen penetration and sufficient in-cylinder mixing. Such pressures lead to chocked flow conditions during the injection process which result in the formation of turbulent under-expanded hydrogen jets. In this context, fundamental understanding of the under-expansion process and turbulent mixing just after the nozzle exit is necessary for the successful design of an efficient hydrogen injection system and associated injection strategies. The current study used large eddy simulation (LES) to investigate the characteristics of hydrogen under-expanded jets with different nozzle pressure ratios (NPR), namely 8.5, 10, 30 and 70. A test case of methane injection with NPR = 8.5 was also simulated for direct comparison with the hydrogen jetting under the same NPR. The near-nozzle shock structure, the geometry of the Mach disk and reflected shock angle, as well as the turbulent shear layer were all captured in very good agreement with data available in the literature. Direct comparison between hydrogen and methane fuelling showed that the ratio of the specific heats had a noticeable effect on the near-nozzle shock structure and dimensions of the Mach disk. It was observed that with methane, mixing did not occur before the Mach disk, whereas with hydrogen high levels of momentum exchange and mixing appeared at the boundary of the intercepting shock. This was believed to be the effect of the high turbulence fluctuations at the nozzle exit of the hydrogen jet which triggered Gortler vortices. Generally, the primary mixing was observed to occur after the location of the Mach disk and particularly close to the jet boundaries where large-scale turbulence played a dominant role. It was also found that NPR had significant effect on the mixture's local fuel richness. Finally, it was noted that applying higher injection pressure did not essentially increase the penetration length of the hydrogen jets and that there could be an optimum NPR that would introduce more enhanced mixing whilst delivering sufficient fuel in less time. Such an optimum NPR could be in the region of 100 based on the geometry and observations of the current study.     

Recent progress in the use of hydrogen as a fuel for internal combustion engines

Hydrogen-fueled internal combustion engines (H₂ICEs) have been the topic of research for many decades, and contemporary reviews have surveyed the relevant literature. Because of a number of relatively large R&D projects that have been ongoing recently, much progress has been made that is worth reporting. Specifically, this paper reviews the advancements made in plotting the possibilities offered by direct injection of hydrogen, in-cylinder heat transfer, modeling and combustion strategies (on an engine as well as vehicle level). These efforts have resulted in impressive efficiency numbers, both at peak and part load operation, while keeping emissions far below regulatory limits and reaching satisfactory specific power outputs. New demonstration vehicles have been put on the road showing the relatively low barriers (on a vehicle level) to introduce hydrogen engined transportation and these are briefly described. The paper discusses the merits of H₂ICEs but also what makes them potentially unfit as a realistic alternative. Finally, the paper concludes with the main areas of research that require further efforts.     

Effect of choice of pilot fuel on the performance of natural gas in diesel engines

Energy conversion alone is inadequate to satisfy long-term energy demands and to gain independence from petroleum-based fuels. It is, therefore, of great importance that all potential fuel alternatives be recognised and examined. Natural gas and bio-liquids may provide such alternatives and their potential has been examined (Nwafor and Rice, WREC 1994;2:841). Fossil fuel combustion is the main culprit in environmental pollution, whilst the impacts of vegetable oil fuel systems are on the whole less adverse and more localised than those of fossil fuels. This paper investigates the possibility of substituting a plant fuel pilot injection for diesel fuel for combustion of natural gas in a diesel engine. The pilot fuels used are rape methyl ester (RME) and neat rapeseed oil. The test results indicate that engine performance on these alternative pilot fuels was satisfactory and compared favourably with the baseline test result on diesel fuel.     

Engine characteristics of emissions and performance using mixtures of natural gas and hydrogen

An evaluation was performed on the efficiency and emissions from an engine fuelled with compressed natural gas (CNG) and a mixture of natural gas and hydrogen, respectively. The mixtures of CNG and hydrogen were named HCNG.     

Comparison of performance and emissions of a supercharged dual-fuel engine fueled by hydrogen and hydrogen-containing gaseous fuels

This study investigated the engine performance and emissions of a supercharged engine fueled by hydrogen (H₂), and three other hydrogen-containing gaseous fuels such as primary fuels, and diesel as pilot fuel in dual-fuel mode. The energy share of primary fuels was about 90% or more, and the rest of the energy was supplied by diesel fuel. The hydrogen-containing fuels tested in this study were 13.7% H₂-content producer gas, 20% H₂-content producer gas and 56.8% H₂-content coke oven gas (COG). Experiments were carried out at a constant pilot injection pressure and pilot quantity for different fuel-air equivalence ratios and at various injection timings. The experimental strategy was to optimize the pilot injection timing to maximize engine power at different fuel-air equivalence ratios without knocking and within the limit of the maximum cylinder pressure. Better thermal efficiency was obtained with the increase in H₂ content in the fuels, and neat H₂ as a primary fuel produced the highest thermal efficiency. The fuel-air equivalence ratio was decreased with the increase in H₂ content in the fuels to avoid knocking. Thus, neat H₂-operation produced less maximum power than other fuels, because of much leaner operations. Two-stage combustion was obtained; this is an indicator of maximum power output conditions and a precursor of knocking combustion. The emissions of CO and HC with neat H₂-operation were 98-99.9% and NOx about 85-90% less than other fuels.     

Evaluation of a new computational fluid dynamics model for internal combustion engines using hydrogen under motoring conditions

The present work conducts a preliminary evaluation of a new CFD (computational fluid dynamics) model, which is under development at the authors' laboratory. Using this model, it is feasible to understand how the intake manifold and in-cylinder geometry affect the in-cylinder flow field and the mixing processes taking place in an Otto (spark-ignition) engine. The model is applied on a high-swirl, two-valve, four-stroke, transparent combustion chamber engine running under motoring conditions. To investigate the fuel–air mixing process, hydrogen is injected in the intake manifold. To evaluate the model three case studies are examined. First, the model is applied to simulate the external mixing in the intake manifold with a tee-mixer injection system. Secondly, the transient gas flow field in the intake manifold and engine cylinder is examined over the complete engine cycle. Finally, the transient mixing process in the intake manifold and the spatial and temporal distribution of species concentrations inside the cylinder are numerically computed using the developed model. To validate the model, the results obtained through the test cases examined are compared either with available experimental data or with simulated results, which are obtained using a commercially available CFD code applied under the same conditions.     

进气道喷水对高强化柴油机燃烧与排放特性的影响

针对高转速和大负荷工况下发动机粗暴燃烧、热负荷过高的问题,在一台高强化单缸柴油机上加装进气道辅助喷水系统进行仿真试验,研究了进气道喷水对燃烧与排放特性的影响。通过建立一维热力学模型和三维全气道模型,在独立进气道水喷射系统的高强化单缸柴油机上进行试验,对比不同喷水压力和水油比对缸内氧气浓度、燃烧压力、燃烧温度和NOx排放的影响。试验结果表明,喷水压力为1 MPa、水油比为0.6时,缸内最高燃烧温度降低34.2 K,NOx生成量减少24.6%。进气道喷水可明显降低缸内燃烧温度,在优化排放的同时有效改善了高强化柴油机热负荷过高的问题。     

An onboard hydrogen generator for hydrogen enhanced combustion with internal combustion engine

Hydrogen enhanced combustion (HEC) for internal combustion engine is known to be a simple mean for improving engine efficiency in fuel saving and cleaner exhaust. An onboard compact and high efficient methanol steam reformer is made and installed in the tailpipe of a vehicle to produce hydrogen continuously onboard by using the waste heat of the engine for heating up the reformer; this provides a practical device for the HEC to become a reality. This use of waste heat from engine enables an extremely high process efficiency of 113% to convert methanol (8.68 MJ) for 1.0 NM of hydrogen (9.83 MJ) and low cost of using hydrogen as an enhancer or as a fuel itself. The test results of HEC from the onboard hydrogen production are presented with 2 gasoline engine vehicles and 2 diesel engines; the results indicate a hike of engine efficiency in 15–25% fuel saving and a 40–50% pollutants reduction including 70% reduction of exhaust smoke. The use of hydrogen as an enhancer brings about 2–3 fold of net reductions in energy, carbon dioxide emission and fuel cost expense over the input of methanol feed for hydrogen production.     

涡流室式LPG柴油双燃料发动机燃烧模型

根据涡流室、主燃室中气体流动过程的质量和能量的交换关系 ,建立了涡流室式 LPG ( liquefiedpetrdeum gas) /柴油双燃料发动机准维燃烧模型的方程 ,提出了如何使两种不同性质燃料的燃烧在同一个燃烧过程中相互联系、相互作用的燃烧模型。根据模型提供的方程 ,对缸内燃烧过程和 NOx 的生成进行了模拟仿真 ,将其同发动机台架试验的结果进行了验证、分析和讨论。     

Increasing the power output of hydrogen internal combustion engines by means of supercharging and exhaust gas recirculation

Spark ignition engines can be relatively easily converted to hydrogen using port fuel injection (PFI). However, because of the lower volumetric energy density of a hydrogen–air mixture and the occurrence of abnormal combustion phenomena such as backfire, hydrogen-fueled PFI engines suffer from a power deficit in comparison with gasoline engines. This paper reports measurements on a single-cylinder hydrogen engine equipped with a supercharger and an exhaust gas recirculation (EGR) system. Using EGR combined with supercharging and a three-way catalyst (TWC) is shown to significantly increase the power output while limiting tailpipe emissions of oxides of nitrogen (NO_x).     

植物油及其衍生物在柴油机上的应用

评述了植物油及其衍生物在柴油机上应用的前景和可行性,讨论了目前纯植物油、生物柴油和它们的混合物在柴油机上使用的最新研究成果。比较了植物油及其衍生物和传统柴油的性质以及柴油机燃用这些燃料时的性能和排放特性。     

The effect of HRG gas addition on diesel engine combustion characteristics and exhaust emissions

Extensive studies have been dedicated in the last decade to the possibility to use hydrogen in the dual-fuel mode to improve combustion characteristics and emissions of a diesel engine. The results of these studies, using pure hydrogen or hydrogen containing gas produced through water electrolysis, are notably different.The present investigation was conducted on a tractor diesel engine running with small amounts of the gas—provided by a water electrolyzer—aspirated in the air stream inducted in the cylinder. The engine was operated at light and medium loads and various speeds.It was found that the addition of HRG gas has a slight negative impact, up to 2%, on the engine brake thermal efficiency. Smoke is significantly reduced, up to 30%, with HRG enrichment, while NO_x concentrations vary in both senses, up to 14%, depending on the engine operation mode. A relative small amount of HRG gas can be used with favorable effects on emissions and with a small penalty in thermal efficiency.