DME-LPG混合燃料的试验研究

通过在火花点火式发动机燃用二甲醚混合燃料与汽油的对比试验,评价了二甲醚混合燃料的不同组份在发动机上的应用特性,分析了由二甲醚、液化石油气和甲醇组成的两种配比混合燃料的经济性能、动力性能及怠速时的排放性能。结果表明,发动机燃用二甲醚—液化石油气混合燃料基本达到了燃用汽油的水平。     

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.     

Effect of hydrogen addition on combustion and emissions performance of a spark-ignited ethanol engine at idle and stoichiometric conditions

Regarding the limited fossil fuel reserves, the renewable ethanol has been considered as one of the substitutional fuels for spark ignition (SI) engines. But due to its high latent heat, ethanol is usually hard to be well evaporated to form the homogeneous fuel–air mixture at low temperatures, e.g., at idle condition. Compared with ethanol, hydrogen possesses many unique combustion and physicochemical properties that help improve combustion process. In this paper, the performance of a hydrogen-enriched SI ethanol engine under idle and stoichiometric conditions was investigated. The experiment was performed on a modified 1.6 L SI engine equipped with a hydrogen port-injection system. The ethanol was injected into the intake ports using the original engine gasoline injection system. A self-developed hybrid electronic control unit (HECU) was adopted to govern the opening and closing of hydrogen and ethanol injectors. The spark timing and idle bypass valve opening were governed by the engine original electronic control unit (OECU), so that the engine could operate under its original target idle speed for each testing point. The engine was first fueled with the pure ethanol and then hydrogen volume fraction in the total intake gas was gradually increased through increasing hydrogen injection duration. For a specified hydrogen addition level, ethanol flow rate was reduced to keep the hydrogen–ethanol–air mixture at stoichiometric condition. The test results showed that hydrogen addition was effective on reducing cyclic variations and improving indicated thermal efficiency of an ethanol engine at idle. The fuel energy flow rate was reduced by 20% when hydrogen volume fraction in the intake rose from 0% to 6.38%. Both flame development and propagation periods were shortened with the increase of hydrogen blending ratio. The heat transfer to the coolant was decreased and the degree of constant volume combustion was enhanced after hydrogen addition. HC and CO emissions were first reduced and then increased with the increase of hydrogen blending fraction. The acetaldehyde emission from the hydrogen-enriched ethanol engine is lower than that from the pure ethanol engine. However, the addition of hydrogen tended to increase NO_x emissions from the ethanol engine at idle and stoichiometric conditions.     

二甲醚发动机动力及排放性能研究

在一台车用单缸直喷柴油机上进行了燃用二甲醚的试验研究,结果表明:二甲醚发动机的动力性及排放性能优于柴油机.基于二甲醚燃烧数值仿真计算平台,建立氮氧化物模型.利用建立的平台计算二甲醚发动机在不同负荷下的动力及排放性能.得出:仿真结果与试验结果相同.研究结果表明:二甲醚发动机的NOx排放比柴油机大幅度降低,二甲醚发动机可以完全消除碳烟排放,二甲醚是一种可以替代柴油的理想清洁燃料.     

Effect of hydrogen addition on the idle performance of a spark ignited gasoline engine at stoichiometric condition

With regard to the improvement of efficiency, combustion stability, and emissions in a gasoline engine at idle condition, an experimental study aimed at improving engine idle performance through hydrogen addition was carried out on a 4-cylinder gasoline-fueled spark ignited (SI) engine. The engine was modified to be fueled with the mixture of gasoline and hydrogen injected into the intake ports simultaneously. A self-developed electronic control unit (DECU) was dedicatedly used to control the injection timings and injection durations of gasoline and hydrogen. Other parameters, such as spark timing and idle valve opening, were controlled by the original engine electronic control unit (OECU). Various hydrogen enrichment levels were selected to investigate the effect of hydrogen addition on engine speed fluctuation, thermal efficiency, combustion characteristics, cyclic variation and emissions under idle and stoichiometric conditions. The experimental results showed that thermal efficiency, combustion performance, NO_x emissions are improved with the increase of hydrogen addition level. The HC and CO emissions first decrease with the increasing hydrogen enrichment level, but when hydrogen energy fraction exceeds 14.44%, it begins to increase again at idle and stoichiometric conditions.     

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.     

Emissions and fuel consumption characteristics of an HCNG-fueled heavy-duty engine at idle

The idle performance of an 11-L, 6-cylinder engine equipped with a turbocharger and an intercooler was investigated for both compressed natural gas (CNG) and hydrogen-blended CNG (HCNG) fuels. HCNG, composed of 70% CNG and 30% hydrogen in volume, was used not only because it ensured a sufficient travel distance for each fueling, but also because it was the optimal blending rate to satisfy EURO-6 emission regulation according to the authors' previous studies. The engine test results demonstrate that the use of HCNG enhanced idle combustion stability and extended the lean operational limit from excess air ratio (λ) = 1.5 (CNG) to 1.6. A decrease of more than 25% in the fuel consumption rate was achieved in HCNG idle operations compared to CNG. Total hydrocarbon and carbon monoxide emissions decreased when fueled with HCNG at idle because of the low carbon content and enhanced combustion characteristics. In particular, despite hydrogen enrichment, less nitrogen oxides (NO_x) were emitted with HCNG operations because the amount of fuel supplied for a stable idle was lower than with CNG operations, which eventually induced lower peak in-cylinder combustion temperature. This low HCNG fuel quantity in idle condition also induced a continuous decrease in NO_x emissions with an increase in λ. The idle engine test results also indicate that cold-start performance can deteriorate owing to low exhaust gas temperature, when fueled with HCNG. Therefore, potential solutions were discussed, including combustion strategies such as retardation of spark ignition timing combined with leaner air/fuel ratios.     

Influence of pentanol and dimethyl ether blending with diesel on the combustion performance and emission characteristics in a compression ignition engine under low temperature combustion mode

Dimethyl ether (DME) and n-pentanol can be derived from non-food based biomass feedstock without unsettling food supplies and thus attract increasing attention as promising alternative fuels, yet some of their unique fuel properties different from diesel may significantly affect engine operation and thus limit their direct usage in diesel engines. In this study, the influence of n-pentanol, DME and diesel blends on the combustion performance and emission characteristics of a diesel engine under low-temperature combustion (LTC) mode was evaluated at various engine loads (0.2–0.8 MPa BMEP) and two Exhaust Gas Recirculation (EGR) levels (15% and 30%). Three test blends were prepared by adding different proportions of DME and n-pentanol in baseline diesel and termed as D85DM15, D65P35, and D60DM20P20 respectively. The results showed that particulate matter (PM) mass and size-resolved PM number concentration were lower for D85DM15 and D65P35 and the least for D60DM20P20 compared with neat diesel. D60DM20P20 turned out to generate the lowest NO_x emissions among the test blends at high engine load, and it further reduced by approximately 56% and 32% at low and medium loads respectively. It was found that the combination of medium EGR (15%) level and D60DM20P20 blend could generate the lowest NO_x and PM emissions among the tested oxygenated blends with a slight decrease in engine performance. THC and CO emissions were higher for oxygenated blends than baseline diesel and the addition of EGR further exacerbated these gaseous emissions. This study demonstrated a great potential of n-pentanol, DME and diesel (D60DM20P20) blend in compression ignition engines with optimum combustion and emission characteristics under low temperature combustion mode, yet long term durability and commercial viability have not been considered.     

Reducing the idle speed of an SI CNG engine fueled by HCNG with high hydrogen ratio

This paper presents an experimental study aimed at idle characteristics of a CNG engine fueled by HCNG with 55% hydrogen blend. The idle speed was reduced from original 800 r/min to 750 r/min and 700 r/min, and the characteristics of combustion & emissions at reduced idle speed were investigated. It is found that, for the HCNG engine, only reducing idle speed cannot reduce fuel consumption at conditions of fixed λ. In order to reduce fuel consumption and keep the COV at rather low levels, the excess air ratio must be increased properly while reducing the engine idle speed. Due to the large valve overlap (30°) of this inlet inject HCNG engine, CH₄ emissions are mainly caused by scavenging, which account for the vast majority of THC emissions. The emissions of CO, THC and NOx are reduced with the decrease of ignition advance angle at a fixed λ.     

Biodiesel production from inedible animal tallow and an experimental investigation of its use as alternative fuel in a direct injection diesel engine

In this study, a substitute fuel for diesel engines was produced from inedible animal tallow and its usability was investigated as pure biodiesel and its blends with petroleum diesel fuel in a diesel engine. Tallow methyl ester as biodiesel fuel was prepared by base-catalyzed transesterification of the fat with methanol in the presence of NaOH as catalyst. Fuel properties of methyl ester, diesel fuel and blends of them (5%, 20% and 50% by volume) were determined. Viscosity and density of fatty acid methyl ester have been found to meet ASTM D6751 and EN 14214 specifications. Viscosity and density of tallow methyl esters are found to be very close to that of diesel. The calorific value of biodiesel is found to be slightly lower than that of diesel. An experimental study was carried out in order to investigate of its usability as alternative fuel of tallow methyl ester in a direct injection diesel engine. It was observed that the addition of biodiesel to the diesel fuel decreases the effective efficiency of engine and increases the specific fuel consumption. This is due to the lower heating value of biodiesel compared to diesel fuel. However, the effective engine power was comparable by biodiesel compared with diesel fuel. Emissions of carbon monoxide (CO), oxides of nitrogen (NO_x), sulphur dioxide (SO₂) and smoke opacity were reduced around 15%, 38.5%, 72.7% and 56.8%, respectively, in case of tallow methyl esters (B100) compared to diesel fuel. Besides, the lowest CO, NO_x emissions and the highest exhaust temperature were obtained for B20 among all other fuels. The reductions in exhaust emissions made tallow methyl esters and its blends, especially B20 a suitable alternative fuel for diesel and thus could help in controlling air pollution. Based on this study, animal tallow methyl esters and its blends with petroleum diesel fuel can be used a substitute for diesel in direct injection diesel engines without any engine modification.     

汽车发动机怠速稳定性模糊控制系统试验研究

怠速工况运行品质是影响汽车发动机的经济性和排放性能的重要因素.在完成目标发动机喷油、点火系统控制匹配的基础上,以提高怠速运行稳定性为目标开发了怠速模糊控制器,编写了输入变量的模糊化、模糊推理过程以及模糊输出量的精确化等控制软件.采用模糊控制可以避免因汽车发动机怠速运行工况复杂造成难以建立精确数学模型,且可在发动机怠速工况时对转速进行较好的控制.发动机台架试验结果表明,采用模糊控制能有效改善汽车发动机的怠速运转稳定性,怠速运行质量显著提高.     

Study of spark ignition engine fueled with methanol/gasoline fuel blends

A 3-cylinder port fuel injection engine was adopted to study engine power, torque, fuel economy, emissions including regulated and non-regulated pollutants and cold start performance with the fuel of low fraction methanol in gasoline. Without any retrofit of the engine, experiments show that the engine power and torque will decrease with the increase fraction of methanol in the fuel blends under wide open throttle (WOT) conditions. However, if spark ignition timing is advanced, the engine power and torque can be improved under WOT operating conditions. Engine thermal efficiency is thus improved in almost all operating conditions. Engine combustion analyses show that the fast burning phase becomes shorter, however, the flame development phase is a little delay.When methanol/gasoline fuel blends being used, the engine emissions of carbon monoxide (CO) and hydrocarbon (HC) decrease, nitrogen oxides (NO_x) changes little prior to three-way catalytic converter (TWC). After TWC, the conversion efficiencies of HC, CO and NO_x are better. The non-regulated emissions, unburned methanol and formaldehyde, increase with the fraction of methanol, engine speed and load, and generally the maximum concentrations are less than 200 ppm. Experimental tests further prove that methanol and formaldehyde can be oxidized effectively by TWC. During the cold start and warming-up process at 5 °C, with methanol addition into gasoline, HC and CO emissions decrease obviously. HC emission reduces more than 50% in the first few seconds (cold start period) and nearly 30% in the following warming-up period, CO reduces nearly 25% when the engine is fueled with M30. Meanwhile, the temperature of exhaust increases, which is good to activate TWC.     

Experimental study of hydrogen enriched compressed natural gas (HCNG) engine and application of support vector machine (SVM) on prediction of engine performance at specific condition

The effect of excess air ratio (λ) and ignition advance angle (θ_ig) on the combustion and emission characteristics of hydrogen enriched compressed natural gas (HCNG) on a 6-cylinder compressed natural gas (CNG) engine has been experimental studied in an engine test bench, aiming at enriching the sophisticated calibration of HCNG fueled engine and increasing the prediction accuracy of the SVM method on automobile engines. Three different fuel blends were selected for the experiment: 0%, 20% and 40% volumetric hydrogen blend ratios. It is noted that combustion intensity varies with the excess air ratio and the ignition advance angle, so are the emissions. The optimal value of λ or θ_ig has been explored in the specific engine condition. Results show that blending hydrogen can enhance and advance the combustion and stability of CNG engine, and it also has some benefic influence on the emissions such as reducing the CO and CH₄. Meanwhile, a simulation research on forecasting the engine performance by using the support vector machine (SVM) method was conducted in detail. The torque, brake specific fuel consumption and NO_x emission have been selected to characterize the power, economic and emissions of the engine with various HCNG fuels, respectively. It can be seen that the optimal model built by the SVM method can highly describe the relationship of the engine properties and condition parameters, since the value of the complex correlation coefficient is larger than 0.97. Secondly, the prediction performance of the optimal model for torque or BSFC is much better than the case of NO_x. Besides, the optimal model built by the PSO optimization method has the best prediction accuracy, and the accuracy of the model obtained based on the training group with 20% hydrogen blend ratio is the best compared with those of others. The upshots in this article provide experimental support and theoretical basis for the adoption of HCNG fuel on internal combustion engines as well as the application of intelligent algorithmic in the engine calibration technology field.     

甲醇-汽油混合燃料对汽油机性能影响的试验研究

在一台多点电喷汽油机上,开展了燃用不同掺混比的甲醇-汽油混合燃料时发动机的经济性、排放特性研究。结果表明:电喷汽油机燃用低掺混比甲醇-汽油(小于30%)时,随着甲醇掺混比的增加,经济性有所改善,有效热效率明显提高;CO的排放有明显改善,中低负荷时HC排放有所改善,高负荷时HC排放增加,NOx排放相当,而怠速工况时,排放特性变差。     

甲醇和二甲醚燃料在发动机中的应用现状

论述了我国发展甲醇和二甲醚燃料的必要性,并分析了甲醇和二甲醚(DME)作为发动机燃料的优势和不利因素,详细阐述了目前汽油机、柴油机和HCCI发动机燃用甲醇和二甲醚燃料的现状,指出了今后发动机代用燃料的发展方向。     

Effect of methanol fumigation on performance and emission characteristics in a waste cooking oil-fuelled single cylinder CI engine

Use of bio-oils in diesel engines results in increased NOx and smoke and reduced brake thermal efficiency. Dual-fuel engines can use a wide range of fuels mainly alcohols and yet operate with high thermal efficiency and simultaneous reduction of NO and smoke emissions. The present study aims to explore the effect of methanol–waste cooking oil (WCO) dual-fuel mode on performance and emission characteristics in a single cylinder Compression ignition (CI) engine producing 3.7 kW at 1,500 rpm. WCO was injected in the conventional injection system, replacing diesel as pilot fuel. Methanol was fumigated along with intake air using a variable jet carburetor, which was installed in the inlet manifold. The methanol was fumigated, and the energy share was varied for each load till the knock limit. Performance parameters like brake thermal efficiency (BTE) and emission parameters like HC, CO, NO, and smoke emissions were tested for various energy shares of methanol with WCO as a pilot fuel. The results show that an increase in methanol fumigation reduced BTE at lower loads. At 75% and 100% load conditions, BTE was higher with methanol addition. The maximum BTE was observed for 38% methanol share, which is about 11% higher, compared to WCO at 100% load condition. Methanol fumigation aided in the simultaneous reduction of NO and smoke emission, and the maximum reduction was occurred with 51% methanol share at 100% load condition. HC and CO emissions were higher at all load conditions with methanol fumigation.     

Effect of hydrogen enrichment on performance,combustion, and emission of a methanol fueled SI engine

The study of potentially high rated alternative fuel (Methanol) for the IC engines is an exciting topic in the recent research advancement. However, the study of combination of methanol and hydrogen is considered to address both economic and environmental needs. Hydrogen with best combustion characteristics will compensate for the drawbacks of methanol as a fuel. In the present investigation hydrogen enrichment to methanol has shown a significant enhancement in performance and combustion; the overall emission has reduced substantially. The experiments for a different set of trials, including hydrogen enrichment ranging between 5% and 20% with 2.5% increment, the engine is operated with wide-open throttle (WOT) condition for different speeds. The increase in enrichment of hydrogen has shown a rise in BTE, BP, and a reduced BSEC value. The percentage increase in BTE is between 20 and 30%, and an increase in hydrogen beyond 12.5% would affect the volumetric efficiency, and thus performance declines after that. The exhaust emissions have a huge impact on hydrogen enrichment; CO, HC, and CO₂ emission are reduced by 30–40%; however, an increase in cylinder temperature due to rapid combustion slightly increases the NO_x emission. Thus hydrogen enriched methanol operating at higher compression ratio can improve the overall engine characteristics significantly.     

Effect of addition of di-tert butyl peroxide (DTBP) on performance and exhaust emissions of dual fuel diesel engine with hydrogen as a secondary fuel

Today, the world faces a number of challenges on global level. The optimum replacement for fossil fuels is one of these challenges. Hydrogen in the past has been and continues to be used by numerous researchers in diesel engines. However, high NO_x emissions and low replacement of hydrogen fuel are the concern with many researchers. In the present study, di-tert butyl peroxide (DTBP) has been used as an additive in diesel fuel, to investigate the performance and exhaust emissions of the diesel engine working on dual fuel mode by using hydrogen as secondary fuel. At low, medium and high load conditions, the maximum increase in brake thermal efficiency was observed to be 87.50%, 14.68% and 5.89% respectively for 1%, 3% and 5% of additive (DTBP) by 40% of hydrogen fuel substitution, as compared to diesel fuel operation. Moreover, by addition of 4% di-tert butyl peroxide (DTBP) in diesel engine working on dual fuel mode showed 33.82%, 10.27% and 29.27% reduction in NO_x emission at low, medium and high load conditions respectively at 40% hydrogen substitution, as compared to dual fuel operation using hydrogen as secondary fuel without additives. By addition of 5% additive (DTBP) at 69% load condition and 40% hydrogen substitution, reduces CO emissions by 38.66% as compared to dual fuel operation, using hydrogen as secondary fuel.     

Investigation of a hydrogen-assisted combustion system for a light-duty diesel vehicle

Two sets of experiments were conducted to investigate the effects of adding gaseous hydrogen to the intake of compression–ignition (CI) engines fueled with 20% bio-derived/80% petroleum-derived diesel fuel (B20). A 1.3 L, 53 kW CI engine coupled to an eddy-current engine dynamometer was tested first. Data were collected on engine operating parameters, fuel consumption, concentration of total oxides of nitrogen (NO_x) in the exhaust, and exhaust temperature. Eight steady-state operating points were tested with hydrogen flow rates equivalent to 0%, 5%, and 10% of the total fuel energy. In a second set of experiments, the stock gasoline engine of a 2005 Chevrolet Equinox was replaced with a 1.3 L, 66 kW CI engine, and urban drive cycles were run on a chassis dynamometer. The drive cycles were repeated with 0%, 5% and 10% of the fuel energy coming from the fumigated hydrogen. In both experiments, the addition of hydrogen did not result in discernable differences in engine efficiency. In the vehicle testing, there were no noticeable differences in drivability. There were modest reductions in NO_x emissions and increases in exhaust temperature with hydrogen addition. This investigation demonstrates that fumigating relatively small amounts of hydrogen into the intake of a modern diesel engine results in only modest changes in combustion efficiency and emissions with no detrimental effects on vehicle performance or drivability. This strategy can be used to partially offset the use of petroleum-based fuels in light-duty transportation vehicles.     

Idle performance of a hydrogen/gasoline rotary engine at lean condition

Because of the limit of properties of gasoline and irregular design of chamber, the pure gasoline rotary engine generally encounters partial burning, increased noxious emissions or even misfire at lean conditions. This situation could be deteriorated at idle because of the high variation in the intake charge and low combustion temperature. Hydrogen addition is proved to remit the deterioration of performance of sparked-ignited (SI) engines at idle and lean conditions. This paper conducted an experiment on a modified rotary engine equipped with gasoline and hydrogen port-injection systems to explore the performance of a hydrogen–gasoline rotary engine (HGRE) at idle and lean conditions. An electronic management unit (EMU) was invented to manage spark and fuel injection. Excess air ratio (λ) and hydrogen volumetric fraction in the total intake (${\alpha }_{{\text{H}}_2}$) were also governed through the EMU. For this study, the HGRE was operating at idle and ${\alpha }_{{\text{H}}_2}$ was kept at 0% and 3%, respectively. For a specific ${\alpha }_{{\text{H}}_2}$, gasoline flow rate was reduced to make the HGRE run at desired λ. Results indicated that engine fluctuation and fuel energy flow rate were both decreased after hydrogen addition. Combustion duration was cut down and central heat release point was advanced after hydrogen addition. Peak chamber temperature (T_max), pressure and heat release were enhanced after hydrogen blending. HC, CO and CO₂ emissions were simultaneously reduced because of hydrogen enrichment. Specifically, at λ = 1.00, HC, CO and CO₂ emissions were respectively reduced from 42,411 to 26,316 ppm, 1.86 to 0.78% and 9.96 to 8.58% when 3% hydrogen was added.