Study on combustion and emissions of a turbocharged compression ignition engine fueled with dimethyl ether and biodiesel blends

In this study, combustion and emissions characteristics of a turbocharged compression ignition engine fueled with dimethyl ether (DME) and biodiesel blends are experimentally investigated. The effects of nozzle parameter on combustion and emissions are evaluated. The result shows that with the increase of DME proportion, ignition delay, the peak in-cylinder pressure, peak heat-release rate, peak in-cylinder temperature decrease, and their phases retard. Compared to the nozzle 6 × 0.40 mm, the peak cylinder pressure and peak heat-release rate are higher with nozzle 6 × 0.35 mm, and their phases are advanced. Increased DME proportion in fuel blends causes greater differences. Compared to biodiesel, NO_x emissions of blends significantly decrease; HC emissions and CO emissions increase slightly. DME–biodiesel blends can be used as an alternative in a turbocharged CI engine. To obtain low NO_x emissions and a soft engine operation, for high DME proportion blended fuels, nozzle of 6 × 0.40 mm adopted.     

Effects of octane number on exhaust emissions of a spark ignition engine

This paper deals with the experimental study that aims to examine the effects of octane number of three different fuel oxygenates on exhaust emissions of a typical spark ignition engine. Three commonly used oxygenates, namely methyl tertiary butyl ether (MTBE), methanol, and ethanol, which were blended with a base unleaded fuel in three ratios (10, 15 and 20 vol%), were investigated. The engine emissions of CO, HC, and NO_x were measured under a variety of engine operating conditions using an engine dynamometer set‐up. It is found that generally as the octane number of the fuel increases the CO and HC emissions decrease but the NO_x emission increases for all three blends. Further, for the leaded fuel (RON of 92), as the speed of the engine increases the CO and NO_x emissions decrease but the HC emission decreases. A similar trend was found for MTBE blends also. These emission results are presented in terms of octane number and their effects are discussed in this paper. Copyright © 2002 John Wiley & Sons, Ltd.     

Laminar flame speeds of primary reference fuels and reformer gas mixtures

The laminar flame speeds of neat primary reference fuels (PRFs), n-heptane and iso-octane, PRF blends, reformer gas, and reformer gas/iso-octane/air mixtures are measured over a range of equivalence ratios at atmospheric pressure, using counterflow configuration and digital particle image velocimetry (DPIV). PRF blends with various octane numbers are studied. The synthetic reformer gas mixture employed herein has a composition that would be produced from the partial oxidation of rich iso-octane/air mixture into CO and H₂, namely, 28% H₂, 25% CO, and 47% N₂. Computationally, the experimentally determined laminar flame speeds are simulated using the detailed kinetic models available in the literature. Both experimental and computational results demonstrate that the flame speeds of hydrocarbon/air mixtures increase with addition of a small amount of reformer gas, and the flame speeds of reformer gas/air mixtures are dramatically reduced with addition of a small amount of hydrocarbon fuel. Furthermore, the number density effect of seeding particles on flame speed measurement is assessed, and the experimental uncertainties associated with the present DPIV setup as well as the linear extrapolation method employed herein are discussed.     

Combustion performance and emission reduction characteristics of automotive DME engine system

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

Two-stage ignition in HCCI combustion and HCCI control by fuels and additives

A Rapid Compression Machine (RCM) has been used to study the effects of fuel structure and additives on the Homogeneous Charge Compression Ignition (HCCI) of pure hydrocarbon fuels and mixtures under well-determined conditions. Such information is needed for understanding ignition delays and burning rates in HCCI engines, and “knock” in spark-ignition engines. It is also valuable for validating basic chemical kinetic models of hydrocarbon oxidation. The pure fuels used in the study include: paraffins (n-heptane, iso-octane), cyclic paraffins (cyclohexane, methylcyclohexane), olefins (1-heptene, 2-heptene, 3-heptene), cyclic olefins (cyclohexene, 1,3-cyclohexadiene), and an aromatic hydrocarbon (toluene). The additives were 2-ethyl-hexyl-nitrate and di-tertiary-butyl-peroxide. It was found that fuels which contained the structure -CH₂-CH₂-CH₂- showed two-stage ignition with relatively short ignition delays and that the ignition delay depended strongly on the energy released during the first-stage. For primary reference fuel mixtures (n-heptane + iso-octane), the ignition delay depended only on the molar ratio of n-heptane to oxygen and was independent of the octane number (percent iso-octane). On the other hand, the burn rate depended on both these parameters, which uniquely determine the equivalence ratio. When additives were included in the air/fuel mixtures, the ignition delay was reduced but the burn rate was not affected. These results indicate that for HCCI combustion, the ignition delay and the burn rate can be independently controlled using various fuel mixtures and additives.     

Evaluation of hydrogen-containing NaBH4 and oxygen-containing alcohols (CH3OH,C2H5OH) as fuel additives in a gasoline engine

The aim of this study is to obtain alternative fuels with hydrogen-containing (NaBH₄) and oxygen-containing (ethanol, methanol) fuel additives and to test these fuels in a gasoline engine. For this purpose, each of the NaBH₄ added ethanol and methanol solutions was added to pure gasoline at a volume of 10% and mixed fuels named SE10 and SM10 were obtained, respectively. The obtained SE10 and SM10 mixed fuels were tested in a spark ignition engine and the performance and emission effects of the fuels were compared with the pure gasoline fueled engine test data. When the test results of the mixture fuel engine were compared with the test results of the engine running with pure gasoline, the torque of the SE10 fuel engine decreased compared to the pure gasoline engine, while the torque of the SM10 blended engine increased. In addition, while the exhaust gas temperatures of both blended fuels decreased, their specific fuel consumption and thermal efficiency increased. On the other hand, adding NaBH₄ doped ethanol and methanol solutions to pure gasoline resulted in better combustion, reductions in CO emissions of SE10 and SM10 blended fuels by 31.04% and 53.7%, but CO₂ emissions increased by 11.20% and 19.51% respectively. In addition, NO_x emissions of SE10 and SM10 blended fuels decreased by 15.17% and 8.73%, respectively.     

Intermediate temperature heat release in an HCCI engine fueled by ethanol/n-heptane mixtures: An experimental and modeling study

This study examines intermediate temperature heat release (ITHR) in homogeneous charge compression ignition (HCCI) engines using blends of ethanol and n-heptane. Experiments were performed over the range of 0–50% n-heptane liquid volume fractions, at equivalence ratios 0.4 and 0.5, and intake pressures from 1.4 bar to 2.2 bar. ITHR was induced in the mixtures containing predominantly ethanol through the addition of small amounts of n-heptane. After a critical threshold, additional n-heptane content yielded low temperature heat release (LTHR). A method for quantifying the amount of heat released during ITHR was developed by examining the second derivative of heat release, and this method was then used to identify trends in the engine data. The combustion process inside the engine was modeled using a single-zone HCCI model, and good qualitative agreement of pre-ignition pressure rise and heat release rate was found between experimental and modeling results using a detailed n-heptane/ethanol chemical kinetic model. The simulation results were used to identify the dominant reaction pathways contributing to ITHR, as well as to verify the chemical basis behind the quantification of the amount of ITHR in the experimental analysis. The dominant reaction pathways contributing to ITHR were found to be H-atom abstraction from n-heptane by OH and the addition of fuel radicals to O₂.     

Experimental study of fuel stratification for HCCI high load extension

Fuel stratification has the potential to extend the high load limits of homogeneous charge compression ignition (HCCI) combustion by improving the control over the combustion phase as well as reducing the maximum rate of pressure rise. In this work, experiments were carried out on a single-cylinder engine equipped with a dual-fuel-injection system – a port injector for preparing a homogeneous charge and a direct in-cylinder injector for creating the desired fuel stratification. The homogeneous charge was prepared using gasoline fuel while the fuel stratification was created with the in-cylinder injection of either gasoline or methanol during the compression stroke. The test results indicate that high load extension using gasoline for fuel stratification is limited by the trade-off between CO and NO_x emissions. Weak gasoline stratification leads to an advanced combustion phase and an increase in NO_x emission, while increasing the stratification with a higher quantity of gasoline direct injection, results in a significant deterioration in both the combustion efficiency and the CO emission. Engine tests using methanol for the stratification retarded the ignition timing and prolonged the combustion duration, resulting in a substantial reduction in the maximum rate of pressure rise and the maximum cylinder pressure – a prerequisite for HCCI high load extension. Further tests were then conducted with methanol stratification to extend the HCCI load limit and to optimize the stratified methanol-to-gasoline fuel ratio. Compared to gasoline HCCI, a 50% increase in the maximum IMEP attained was achieved with an acceptable maximum pressure rise rate of 0.5 MPa/°CA while maintaining a high thermal efficiency.     

活性添加剂对高辛烷值燃料HCCI着火时刻与燃烧速率的影响

为研讨活性添加剂过氧化二叔丁基(DTBP)对高辛烷值燃料以HCCI燃烧模式运行时的放热率特征、着火时刻、燃烧持续期和排放特性的影响,在一台单缸发动机上,在辛烷值为90(RON90)(90％的异辛烷和10％的正庚烷)的混合燃料中加入不同比例(0～4％)的DTBP,考察5种燃料在1800r／min下不同负荷时的燃烧特性和排放特性．实验结果表明：RON90中没有添加剂时,只能在高温、高负荷下才能以HCCI燃烧模式运行;在其中加入少量的DTBP后,RON90实现HCCI燃烧的工况范围向低温低负荷下大幅度拓展．各种燃料的HCCI燃烧冷焰反应发生在850K左右,到950K结束,进入负温度系数区(NTC),在1125K左右突破NTC区而发生热着火．随DTBP含量增加,系统温度达到冷焰反应和热焰反应的化学时间尺度缩短,因此着火时刻提前,燃烧持续期缩短,特别是提高了低负荷下的燃烧速率．添加剂使各种当量比下未燃碳氢(UHC)和一氧化碳(CO)排放显著改善,NOx排放也保持在很低的水平．     

Diesel-like and HCCI-like operation of a truck engine converted to hydrogen

In addition to the traditional spark ignition (SI), premixed, gasoline-like and compression ignition (CI), diffusion, Diesel-like operation of internal combustion engines, premixed, homogeneous charge, compression ignition (HCCI) operation has also been proposed to improve the fuel conversion efficiency and reduce the pollutant formation. To be attractive, the operation in HCCI mode has to be coupled with the other traditional operations, being HCCI in general difficult to be controlled and limited to values of the air-to-fuel equivalence ratio λ within a narrow windows set by the lean burn limits with large λ and the peak pressure limits with small λ. Furthermore, the specific kinetics of hydrogen makes this fuel more difficult than other hydrocarbons to work in an engine operating HCCI without assistance. In a recent paper, the design of a 12.8 L in-line six cylinder turbo charged directly injected heavy duty truck Diesel engine fuelled with hydrogen has been discussed. Conversion of a latest Diesel engine with a novel power turbine has been studied replacing the in-cylinder Diesel injector and glow plug with a hydrogen injector and a jet ignition pre-chamber. The pre-chamber is a small volume accommodating another hydrogen injector and a glow plug being connected to the in-cylinder through calibrated orifices. This design permits to operate the engine in four different modes:

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diffusion with jet ignition M₁ - an injection occurs in the jet ignition pre-chamber before the main chamber fuel is injected and the engine operates therefore Diesel-like;

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mixed diffusion/premixed Diesel/gasoline like M₂ - an injection occurs in the jet ignition pre-chamber after only part of the main chamber fuel is injected and mixed with air;

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premixed with jet ignition M₃ - an injection occurs in the jet ignition pre-chamber after the main chamber fuel is injected and mixed with air and the engine operates gasoline-like;

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premixed without jet ignition M₄ - no injection occurs in the jet ignition pre-chamber and the engine operates HCCI-like.

While only the Diesel-like operation was previously considered full load, all the modes including the operation HCCI-like are considered here over the full range of loads where the power turbine is either connected to the crankshaft or disconnected and the exhaust gases pass through this turbine or bypass the turbine.This paper deals with computational rather than experimental work. Computations are made with the latest predictive HCCI model using detailed kinetics of GT-POWER and the well established correlative Wiebe models for Diesel and gasoline combustion. HCCI-like operation is considered over a range of air-to-fuel equivalence ratio λ much wider than usually considered with other fuels being perhaps even more suitable than hydrogen to this operation thanks to the jet ignition assistance.     

The impacts of compression ratio on the performance and emissions of ice powered by oxygenated fuels: A review

Energy sources are becoming a governmental issue, with cost and stable supply as the main concern. Oxygenated fuels production is cheap, simple and eco-friendly, as a well as can be produced locally, cutting down on transportation fuel costs. Oxygenated fuels are used directly in an engine as a pure fuel, or they can be blended with fossil fuel. The most common fuels that are conceded under oxygenated fuels are ethanol, methanol, butanol Dimethyl Ether (DME), Ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and biodiesel that have attracted the attention of researchers. Due to the higher heat of vaporization, high octane rating, high flammability temperature, and single boiling point, the oxygenated fuels have a positive impact on the engine performance, combustion, and emissions by allowing the increase of the compression ratio. Oxygenated fuels also have a considerable oxygen content that causes clean combustion. The aim of this paper was to systematically review the impact of compression ratio (CR) on the performance, combustion and emissions of internal combustion engines (ICE) that are operated with oxygenated fuels that could potentially replace petroleum-based fuels or to improve the fuel properties. The higher octane rating of oxygenated fuels can endure higher compression ratios before an engine starts knocking, thus giving an engine the ability to deliver more power efficiently and economically. One of the more significant findings to emerge from this review study was the slight increases or decreases in power when oxygenated fuel was used at the original CR in ICE engines. Also, CO, HC, and NOx emissions decreased while the fuel consumption (FC) increased. However, at higher CR, the engine performance increased and fuel consumption decreased for both SI and CI engines. It was seen the NOx, CO and CO₂ emissions of oxygenated fuels decreased with the increasing CR in the SI engine, but the HC increased. Meanwhile, in CI engine, the HC, CO and NOx decreased as the CR increased with biodiesel fuel.     

Detailed numerical simulation of syngas combustion under partially premixed combustion engine conditions

Two-dimensional detailed numerical simulation is performed to study syngas/air combustion under partially premixed combustion (PPC) engine conditions. Detailed chemical kinetics and transport properties are employed in the study. The fuel, a mixture of CO and H₂ with a 1:1 molar ratio, is introduced to the domain at two different instances of time, corresponding to the multiple injection strategy of fuel used in PPC engines. It is found that the ratio of the fuel mass between the second injection and the first injection affects the combustion and emission process greatly; there is a tradeoff between NO emission and CO emission when varying the fuel mass ratio. The ignition zone structures under various fuel mass ratios are examined. A premixed burn region and a diffusion burn region are identified. The premixed burn region ignites first, followed by the ignition of mixtures at the diffusion burn region, and finally a thin diffusion flame is formed to burn out the remaining fuel. NO is produced mainly in the premixed burn region, and later from the diffusion burn region in mixtures close to stoichiometry, whereas unburned CO emission is mainly from the diffusion burn region. An optimization of the fuel mass in the two regions can offer a better tradeoff between NO emission and CO emission. The effects of initial temperature and turbulence on the premixed burn and diffusion burn regions are investigated.     

Hydroprocessed vegetable oil as a fuel for transportation sector: A review

Renewable fuels produced from vegetable oils are an attractive alternative to fossil-based fuel. Different type of fuels can be derived from these triglycerides. One of them is biodiesel which is a mono alkyl ester of the vegetable oil. The biodiesel is produced by transesterification of the oil with an alcohol in the presence of a catalyst. Another kind of fuel (which is similar to petroleum-derived diesel) can be produced from the vegetable oil using hydroprocessing technique. This method uses elevated temperature and pressure along with a catalyst to produce a fuel termed as ‘renewable diesel’. The fuel produced has properties that are beneficial for the engine as well as the environment. It has high cetane number, low density, excellent cold flow properties and same materials can be used as are used for engine running on petrodiesel. It can effectively reduce NOx, PM, HC, CO emissions and unregulated emissions as well as greenhouse gases as compared to diesel. The fuel is also beneficial for the after-treatment systems. Trials in the field have shown that the volumetric fuel consumption of renewable diesel is higher than petrodiesel and nearly proportional to the volumetric heating value. The present review focuses on the hydroprocessing technique used for the renewable diesel production and the effect of different parameters such as catalyst, reaction temperature, hydrogen pressure, liquid hourly space velocity (LHSV) and H₂/oil ratio on oil conversion, diesel selectivity, and isomerization. The review also summarizes the effect; renewable diesel has on combustion, performance, and emission characteristics of a compression ignition engine.     

Syngas (H2/CO) in a spark-ignition direct-injection engine. Part 1: Combustion,performance and emissions comparison with CNG

The combustion, performance, and emissions of syngas (H₂/CO) in a four-stroke, direct-injection, spark-ignition engine were experimentally investigated. The engine was operated at various speeds, ranging from 1500 to 2400 rev/min, with the throttle being held in the wide-open position. The start of fuel injection was fixed at 180° before the top dead center, and the ignition advance was set at the maximal brake torque. The air/fuel ratio was varied from the technically possible lowest excess air ratio (λ) to lean operation limits. The results indicated that a wider air/fuel operating ratio is possible with syngas with a very low coefficient of variation. The syngas produced a higher in-cylinder peak pressure and heat-release rate peak and faster combustion than for CNG. However, CNG produced a higher brake thermal efficiency (BTE) and lower brake specific fuel consumption (BSFC). The BTE and BSFC of the syngas were on par to those of CNG at higher speeds. For the syngas, the total hydrocarbon emission was negligible at all load conditions, and the carbon monoxide emission was negligible at higher loads and increased under lower load conditions. However, the emission of nitrogen oxides was higher at higher loads with syngas.     

运行工况对基础燃料均质压燃燃烧过程影响的试验研究

在一台经改装的单缸直喷式柴油机上进行了不同辛烷值基础燃料下发动机转速对均质压燃（HCCI）燃烧特性、工况范围和排放特性影响的试验研究。研究结果表明：发动机转速升高，不同辛烷值燃料着火燃烧时刻推迟，以曲轴转角计算的燃烧持续期延长，高辛烷值燃料的缸内最大爆发压力和缸内温度降低；在中间转速，HCCI实现的最高平均指示压力最大，高转速工况，最高平均指示压力降低；对于低辛烷值燃料，转速对燃烧效率影响不大，转速升高，指示热效率增大；对于高辛烷值燃料，转速升高燃烧效率降低，指示热效率在中间转速最高，高转速降低。排放测试表明，转速升高使得HCCI运转的HC和CO排放都升高，NOx排放则逐渐降低。     

Experimental study of combustion performances and emissions of a spark ignition cogeneration engine operating in lean conditions using different fuels

This work presents an experimental study describing a six-cylinder spark ignition engine running with a lean equivalence ratio, high compression ratio, ignition delay and used in a cogeneration system (heat and electricity production). Three types of fuels; natural gas, pure methane and methane/hydrogen blend (85% CH₄ and 15% H₂ by volume), were used for comparison purposes. Each fuel has been investigated at 1500 rpm and for various engine loads fixed by electrical power output conditions. CO, CO₂, HC, and NOx emissions values, and exhaust gas temperature were measured. The effect of fuel composition on engine characteristics has been studied. The results show, that the hydrogen addition increased HC emissions (around 18%), as well as performance, whilst it reduced NO_x (around 31%), exhaust gas temperature, CO and CO₂.     

Co-oxidation in the auto-ignition of primary reference fuels and n-heptane/toluene blends

Auto-ignition of fuel mixtures was investigated both theoretically and experimentally to gain further understanding of the fuel chemistry. A homogeneous charge compression ignition (HCCI) engine was run under different operating conditions with fuels of different RON and MON and different chemistries. Fuels considered were primary reference fuels and toluene/n-heptane blends. The experiments were modeled with a single-zone adiabatic model together with detailed chemical kinetic models. In the model validation, co-oxidation reactions between the individual fuel components were found to be important in order to predict HCCI experiments, shock-tube ignition delay time data, and ignition delay times in rapid compression machines. The kinetic models with added co-oxidation reactions further predicted that an n-heptane/toluene fuel with the same RON as the corresponding primary reference fuel had higher resistance to auto-ignition in HCCI combustion for lower intake temperatures and higher intake pressures. However, for higher intake temperatures and lower intake pressures the n-heptane/toluene fuel and the PRF fuel had similar combustion phasing.     

异辛烷、乙醇及其混合燃料HCCI燃烧的试验研究和分析

在一台改制的发动机上进行了异辛烷、乙醇及其混合燃料HCCI燃烧的研究。发动机性能用缸内压力评估,研究用的参数包括放热率、平均指示压力和热效率。试验结果表明,乙醇着火时刻早于异辛烷;在乙醇中加入异辛烷可以推迟着火,并导致平均指示压力和热效率的降低;对某种特定燃料,HCCI燃烧的发生主要取决于进气充量温度,初始充量温度的增加将导致HCCI燃烧提前;充量温度低或发动机转速低时,混合气形成质量差,对HCCI燃烧有不良影响;指示热效率为30%~43%,其值高于火花点火发动机;预燃室的存在有利于稳定的HCCI燃烧;超稀充量运行可以显著降低NOx排放。     

Study of ignition delay period of n-Butanol blends with JOME and diesel under static loading conditions

Longer ignition delay results in higher in-cylinder temperature which causes higher NO_X emission. However, limited information available about ignition delay and its importance. In the present work, ignition delay of various fuels and their blends is measured on different offload engine conditions. The experimental setup works between full load engine condition (i.e., 40bar and 400°C) and no load engine condition (i.e., 10bar and 300°C). The effect of injection pressure, in-cylinder temperature and in-cylinder pressure on delay period is analyzed for off engine conditions. The results show that parameter which effects ignition delay most is temperature followed by injection pressure and in-cylinder pressure.     

燃料特性对HCCI发动机燃烧和工况范围影响

在一台改装的4缸直喷柴油机上进行燃料特性对均质压燃(HCCI)燃烧和工况范围影响的试验研究.试验选用6种不同燃料:基础燃料(PRF)、汽油以及基础燃料与乙醇混合物.控制6种发动机运转条件:不同进气温度(tin)、进气压力(pin)和转速.结果表明:在某些运转条件下,汽油着火时刻最早,而在另一些运转条件下,PRF着火时刻最早,这就表明燃料特性对HCCI燃烧过程的影响依赖于发动机运转条件.选用敏感性燃料协同合理的运转条件控制,对于运行工况范围的拓展具有更大潜在优势.CAS0(放热完成50%所对应的曲轴转角)与辛烷值指数(OI)具有很好的相关性,OI越高,着火越晚.然而,使用基础燃料与乙醇的混合物时,OI与着火时刻不具有相关性.