Studies on improving the performance of rubber seed oil fuel for diesel engine with DEE port injection

Use of vegetable oils in diesel engines leads to a marginally inferior performance and higher smoke emissions due to their high viscosity and carbon residue. The performance of vegetable oils can be improved by injecting a small quantity of diethyl ether (DEE) along with air. The main objective of this study is to improve the performance, emission and combustion characteristics of a direct injection diesel engine fuelled with rubber seed oil (RSO) through DEE injection at different flow rates of 100, 150 and 200 g/h. A single cylinder diesel engine with rated output of 4.4 kW at 1500 rpm was converted to operate in the DEE injection mode. DEE was injected into the intake port during suction stroke, while rubber seed oil was injected directly inside the cylinder at the end of compression stroke. The injection timing of DEE was optimized for this mode of operation. Results indicate that the brake thermal efficiency of the engine improves from 26.5% with neat RSO to a maximum of 28.5% with DEE injection rate of 200 g/h. Smoke reduces from 6.1 to 4 BSU with DEE injection at the maximum efficiency flow rate. Hydrocarbon and carbon monoxide emissions are also less with DEE injection. There is an increase in the NO_x emission from 6.9 g/kWh to 9.3 g/kWh at the optimum DEE flow rate. DEE injection with RSO shows higher peak pressure and rate of pressure rise compared to neat RSO. Heat release rate indicates an increase in the combustion rate due to the reduced ignition delay and combustion duration with DEE injection.     

Flow properties of vegetable oil-diesel fuel blends

Straight vegetable oils provide cleaner burning and renewable alternatives to diesel fuel, but their inherently high viscosity compared to petroleum based diesel is undesirable for diesel engines. Lowering the viscosity can be simply achieved by either increasing the temperature of the oil or by blending it with diesel fuel, or both. In this work the rheological properties of diesel fuel and vegetable oil mixtures at different compositions were studied as a function of temperature to determine a viscosity-temperature-composition relationship for use in design and optimization of heating and fuel injection systems used in diesel engines. The vegetable oils used were corn, canola, olive, peanut, soybean and sunflower oils which are of commercial food grade. All the vegetable oils and their blends with No. 2 diesel fuel showed time-independent Newtonian behaviour within the test temperatures between 20 °C and 80 °C. Viscosities of the pure oils and diesel were satisfactorily correlated with temperature by means of the Arrhenius typed relationship. The Arrhenius blending rule was found applicable to describing the composition dependence of viscosity all vegetable oils-diesel blends at a fixed temperature. These relations were combined to develop a simple mixture viscosity model to predict the viscosity of the vegetable oil-diesel blends as functions of temperature and composition based on properties of the pure components.     

Oleochemicals as a fuel: Mechanical and economic feasibility

The status of vegetable oils as diesel fuel substitutes is currently dubious. Although it is fair to consider them as short-term emergency fuels (or, more desirably, low proportion supplements to diesel fuels), they present mechanical problems in long-term use that have not yet been solved. It is preferable to use these oils blended in small proportions with diesel fuels. Indirect-injection diesel engines have had fewer problems than direct-injection engines, whether the tests were performed with pure vegetable oil fuel or with vegetable oil/diesel fuel blends. The economic prospect for these fuels is not promising. In general, they are not and have not been economical alternatives to diesel fuel. Exceptions appear to have occurred recently in Brazil and the Philippines where low local prices for vegetable oils combined with high petroleum prices encouraged officials to use low proportion vegetable oil/diesel fuel blends. Nonetheless, current and long-term trends in petroleum and oilseed prices indicate that these fuels will probably not be price competitive within the near future. Emergency disruption of petroleum supplies completely changes the economic situation. Vegetable oils would be worth much more as a fuel during disruptions than otherwise; thus incentives could be strong to include these oils in the fuel supply, diverting them from the food supply.     

Compression ignition engine modifications for straight plant oil fueling in remote contexts: Modification design and short-run testing

Though many plant oils have a similar energy density to fossil diesel fuel, several properties of plant oils are considerably different from those of diesel. Engine modifications can overcome some of these differences. An engine modification kit has been designed and tested for a slow speed, stationary, indirect-injection diesel engine - the Lister-type CS 6/1, common throughout the developing world. The kit allows waste vegetable oil fueling with similar performance to that of diesel fueling. The kit’s simple yet robust design is targeted for use as a development mechanism, allowing remote farmers to use locally grown plant oils as a diesel substitute.The modification kit includes a preheating system and the tuning of the injector pressure and timing to better atomize given the unique properties of straight plant oils. The design methodology for the modifications is detailed and a suite of performance test results are described including fuel consumption, efficiency, pre-combustion chamber pressure, and various emissions. The results of the study show how a combination of preheating the high pressure fuel line, advancing the injector timing and increasing the injector valve opening pressure allows this engine to efficiently utilize plant oils as a diesel fuel substitute, potentially aiding remote rural farmers with a lower cost, sustainable fuel source - enabling important agro-processing mechanization in parts of the world that needs it most.     

Speed of sound and isentropic bulk modulus of alkyl monoesters at elevated temperatures and pressures

Biodiesel is a biodegradable, sulfur-free, oxygenated, and renewable alternative diesel fuel consisting of the alkyl monoesters of FA from vegetable oils and animal fats. Biodiesel can be used in existing diesel engines without significant modifications. However, differences in physical properties between biodiesel and petroleum-based diesel fuel may change the engine's fuel injection timing and combustion characteristics. These altered physical and chemical properties also may cause the exhaust emissions and performance to differ from the optimized settings chosen by the engine manufacturer. In particular, the density, speed of sound, and isentropic bulk modulus have a significant effect on the fuel injection system and combustion. The objective of this study was to measure these three properties for biodiesel (and the pure esters that are the constituents of biodiesel) at temperatures from 20 to 100°C and at pressures from atmospheric to 32.5 MPa. Ten different biodiesel fuels, 16 different pure FA esters, three hydrocarbons, and one diesel fuel were tested. The measured values of density, speed of sound, and isentropic bulk modulus are presented. Correlations between pressure and temperature are demonstrated. Speed of sound and isentropic bulk modulus tend to increase as the degree of unsaturation increases and as the chain length increases. However, density increased with shorter chain length and decreased with saturation.     

Experimental investigation of diesel engine performance and emission characteristics using jojoba/diesel blend and sunflower oil

Experimental study has been carried out to investigate performance parameters, emissions, cylinder pressure, exhaust gas temperature (T_exhaust) and engine wall temperatures (T_wall) for direct injection diesel engine. Tests were conducted for sunflower oil (S100) and 20% jojoba oil + 80% pure diesel fuel (B20) in comparison to pure diesel fuel with different engine speeds. S100 and B20 were selected for the study because of its being widely used in Egypt and in the world. Also, series of tests are conducted at same previous conditions with different percentage of exhaust gas recirculation (EGR) from 0% to 12% of inlet mass of air fresh charge. Results indicate that S100 or B20 gives lower brake thermal efficiency (η_B), brake power (BP), brake mean effective pressure (BMEP), and higher brake specific fuel consumption (BSFC) due to lower heating value compared to pure diesel fuel. S100 or B20 gives lower NO_X concentration due to lower gas temperature. S100 or B20 gives higher T_wall and T_exhaust due to incomplete combustion inside engine cylinder. S100 or B20 gives higher CO and CO₂ concentrations due to higher carbon/hydrogen ratio. The position of maximum pressure (P_max) change for pure diesel fuel is earlier than for S100 or B20. The results show that S100 or B20 are promising as alternative fuel for diesel engine. The utilization of vegetable oils does not require a significant modification of existing engines. This can be seen as the main advantage of vegetable oils. The main disadvantages of biodiesel fuels are high viscosity, drying with time, thickening in cold conditions, flow and atomization characteristics.     

Cavitation, primary break-up and flash boiling of gasoline, iso-octane and n-pentane with a real-size optical direct-injection nozzle

Improvements to the direct-injection spark-ignition combustion system are necessary if the potential reductions in fuel consumption and emissions are to be fully realized in the near future. One critical link in the optimization process is the design and performance of the injectors used for fuel atomization. Multi-hole injectors have become the state-of-the-art choice for gasoline direct-injection engines due to their flexibility in fuel targeting by selection of the number and angle of the nozzle holes, as well as due to their demonstrated stability of performance under a wide range of operating conditions. Recently there has been increased attention devoted to the study of the flow through the internal passages of injectors because of the presence of particular fluid phenomena, such as large-scale vortical motion and cavitation patterns, which have been shown to influence the characteristics of primary break-up. Understanding how cavitation can be used to improve spray atomisation is essential for optimizing mixture preparation quality under early injection and stratified engine operating conditions but currently no data exist for injector-body temperatures representative of real engine operation, particularly at low-load conditions that can also lead to phase change due to fuel flash boiling. This paper outlines results from an experimental imaging investigation into the effects of fuel properties, temperature and pressure conditions on the extent of cavitation, flash boiling and, subsequently, primary break-up. This was achieved by the use of a real-size transparent nozzle of a gasoline injector from a modern direct-injection combustion system. Gasoline, iso-octane and n-pentane fuels were used at 20 and 90 °C injector-body temperatures for ambient pressures of 0.5 and 1.0 bar in order to simulate early homogeneous injection strategies for part-load and wide-open-throttle engine operation.     

Performance, emission and combustion characteristics of poon oil and its diesel blends in a DI diesel engine

Experimental tests have been carried out to evaluate the performance, emission and combustion characteristics of a diesel engine using Neat poon oil and its blends of 20%, 40%, and 60%, and standard diesel fuel separately. The common problems posed when using vegetable oil in a compression ignition engine are poor atomization; carbon deposits, ring sticking, etc. This is because of the high viscosity and low volatility of vegetable oil. When blended with diesel, poon oil presented lower viscosity, improved volatility, better combustion and less carbon deposit. It was found that there was a reduction in NO_x emission for Neat poon oil and its diesel blends along with a marginal increase in HC and CO emissions. Brake thermal efficiency was slightly lower for Neat poon oil and its diesel blends. From the combustion analysis, it was found that poon oil-diesel blends performed better than Neat poon oil.     

Motorenöle auf der Basis von Pflanzenölen – ein neuer Ansatz

Vegetable oil-based engine oils – A promising start These days most engine lubricants contain petrochemical base oils. A research project looked into the possibility of using vegetable oils and their derivatives (ester oils) for lubrication of four-stroke engines. The environmentally friendly, high-performance engine oils successfully tested in the first project were based on saturated esters and contained a zinc- and polymer-free additive package. Also realized was the second objective of a completely new lubrication concept which allows for the first time the use of unmodified rapeseed or sunflower oil for engine lubrication. The procedures mentioned here compensate for the basically poor ageing resistance of vegetable oils by a progressive renewal of the oil. The used oil is mixed with the fuel and burned without any detrimental effects on exhaust composition. Only low-ash and zinc-free additives were added to the vegetable oils. Initial and positive application know-how was gathered from a number of diesel engines using this combination of special oil and the novel lubrication concept. Environmentally friendly oils being constantly renewed in stationary engines are a promising start.     

Low sooting combustion of narrow-angle wall-guided sprays in an HSDI diesel engine with retarded injection timings

An optically accessible single-cylinder high speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes with narrow-angle wall-guided sprays. Influences of injection timings and injection pressure on combustion characteristics and emissions were studied. In-cylinder pressure was measured and used for heat release analysis. High-speed spray and combustion videos were captured. NO_x emissions were measured in the exhaust pipe. With significantly retarded post-top dead center (TDC) injections, smokeless combustion was achieved for wall-guided diesel spray. Premixed-combustion was observed from the heat release rates and the combustion images. Natural luminosity was found significantly lower for smokeless combustion case. However, NO_x emissions were higher for the low sooting combustion cases. In addition, retarding injection timing lead to more complete combustion with more heat released from the same amount of fuel. Spray images revealed significant fuel impingement for all the conditions and the spray development was controlled and guided by the piston bowl curvature. NO_x and natural luminosity trade-off trend was observed for these conditions. However, quite different from conventional diesel combustion, retarding post-TDC injection timing leads to lower natural luminosity and higher NO_x emissions for narrow-angle wall-guided spray combustion. For the smokeless combustion case under moderate operating load, both homogeneous combustion and low-luminosity pool fires were observed during combustion process and the latter was due to fuel-piston impingement. The findings in this study could be used to solve the smoke issues associated with narrow-angle injection technique under high load conditions. With narrow-angle injectors, ignition could occur for significantly retarded post-TDC injections, which provides a unique mixing approach for diesel engines.     

Efficiencies of various esters of fatty acids as diesel fuels

Methyl esters of commercial grades of lauric, myristic, palmitic, stearic, linoleic and linolenic acids, as well as ethyl and butyl esters of oleic acid, were burned in a diesel engine to determine their efficiencies as fuels. Triolein and some common vegetable oils were burned as comparison fuels and No. 2 diesel fuel was used as a control. The fuels were tested in a single-cylinder direct-injection engine running at rated speed and load in short-term, performance engine tests. Specific fuel consumption and thermal efficiencies of the engine burning these fuels were then determined. Among the methyl esters of the saturated acids, thermal efficiency was inversely related to chain length of the fatty acid. Introduction of a double bond resulted in increased efficiency. Further increases in unsaturation had negligible effects on thermal efficiencies. Ethyl oleate had the highest thermal efficiency and butyl oleate had the lowest thermal efficiency of any of the ester fuels tested. Most of the ester fuels produced higher thermal efficiencies than did No. 2 diesel fuel. Triolein produced the lowest specific fuel consumption of the triglyceride fuels and peanut oil produced the lowest specific fuel consumption of the vegetable oils. The data suggest that ethyl esters of monounsaturated or short-chain fatty acids should make good alternative fuels and that they should be further evaluated in longterm engine tests.     

An experimental study for the effects of boost pressure on the performance and exhaust emissions of a DI-HCCI gasoline engine

As an alternative combustion mode, the HCCI combustion has some benefits compared to conventional SI and CI engines, such as low NO_x emission and high thermal efficiency. However, this combustion mode can produce higher UHC and CO emissions than those of conventional engines. In the naturally aspirated HCCI engines, the low engine output power limits its use in the current engine technologies. Intake air pressure boosting is a common way to improve the engine output power which is widely used in high performance SI and CI engine applications. Therefore, in this study, the effect of inlet air pressure on the performance and exhaust emissions of a DI-HCCI gasoline engine has been investigated after converting a heavy-duty diesel engine to a HCCI direct-injection gasoline engine. The experiments were performed at three different inlet air pressures while operating the engine at the same equivalence ratio and intake air temperature as in normally aspirated HCCI engine condition at different engine speeds. The SOI timing was set dependently to achieve the maximum engine torque at each test condition. The effects of inlet air pressure both on the emissions such as CO, UHC and NO_x and on the performance parameters such as BSFC, torque, thermal and combustion efficiencies have been discussed. The relationships between the emissions are also provided.     

Analytical study for atomization of biodiesels and their blends in a typical injector: Surface tension and viscosity effects

This study presents analytical comparisons of atomization characteristics of 7 biodiesels and 17 binary and ternary blends with D1 and D2 at 80 °C, using a direct injection injector. The atomization of a genetically modified vegetable oil – Captex 355 – and its corresponding biodiesel were also studied. Results from statistical analysis showed that B100 coconut biodiesel had similar atomization characteristics to D2, because of its similar properties, i.e. density, surface tension and viscosity. No significant difference in drop size was observed for all B5 blends, and B20 blends and B100 biodiesels of palm, soybean, cottonseed, peanut and canola. It implies these stocks of biodiesels and their blends can be used in a DI engine with similar atomization characteristics. Ternary biodiesel blends, with ⩽10 wt.% petroleum diesel, can yield equal drop sizes as some binary blends with large quantities of D1 and D2. The ternary biodiesel blends are likely to reduce pollution from exhaust emissions better than the biodiesel blends with D1 or D2. Captex 355 biodiesel had the best atomization characteristics of all the fuels studied. The Sauter mean diameter (SMD) produced by this fuel was up to 13% and 25% smaller than that of D1 and D2, respectively. The Captex 355 biodiesel may be used as a base in binary or ternary biodiesel blends to achieve better atomization than D1 and D2 in diesel engines.     

Diesel/biodiesel proportion for by-compression ignition engines

Nowadays, computational combustion (CC) presents complex mathematical models where the fuel physical properties are important parameters. Most research on biodiesel aims at reducing pollutant emissions placing little emphasis on the relation between the fuel physical properties and its internal combustion. In this work it is presented a brief review on the importance of the physical properties and their relation to the internal combustion proposing a method to determine the volumetric proportion of biodiesel which will have efficient combustion in compression engines. The main injection and atomization properties related to the quality of ignition were measured, such as: density, viscosity and surface tension for mineral diesel (B0), biodiesel (B100) and other eleven mixtures BXX. With the proposed method, it was found that mixtures of diesel/soybean ethylic biodiesel from B2 to B30, present satisfactory internal combustion. The method may be used to predict the behavior of BXX proportions from other animal or vegetable sources and even be used as a preliminary or complementary criterion for the biodiesel certification.     

The speed of sound and isentropic bulk modulus of biodiesel at 21°C from atmospheric pressure to 35 MPa

Biodiesel, an alternative diesel fuel consisting of the alkyl monoesters of fatty acids from vegetable oils and animal fats, can be used in existing diesel engines without modification. However, property changes associated with the differences in chemical structure between biodiesel and petroleumbased diesel fuel may change the engine's injection timing. These injection timing changes can change the exhaust emissions and performance from the optimized settings chosen by the engine manufacturer. This study presents the results of measurements of the speed of sound and the isentropic bulk modulus for methyl and ethyl esters of fatty acids from soybean oil and compares them with No. 1 and No. 2 diesel fuel. Data are presented at 21±1°C and for pressures from atmospheric to 34.74 MPa. The results indicate that the speed of sound and bulk modulus of the monoesters of soybean oil are higher than those for diesel fuel and these can cause changes in the fuel injection timing of diesel engines. Linear equations were used to fit the data as a function of pressure, and the correlation constants are given.     

Comparative environmental behavior of bus engine operating on blends of diesel fuel with four straight vegetable oils of Greek origin: Sunflower, cottonseed, corn and olive

An experimental study is conducted to evaluate the use of sunflower, cottonseed, corn and olive straight vegetable oils (SVO) of Greek origin, in blends with diesel fuel at proportions of 10 vol.% and 20 vol.%, in a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy duty (HD), direct injection (DI), ‘Mercedes-Benz’, mini-bus engine installed at the authors’ laboratory. The series of tests are conducted using each of the above blends, with the engine working at two speeds and three loads. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides (NO_x), carbon monoxide (CO) and total unburned hydrocarbons (HC) are measured. With reference to the corresponding neat diesel fuel operation, the vegetable oil blends show reduction of emitted smoke with slight increase of NO_x and effectively unaffected thermal efficiency. Theoretical aspects of diesel engine combustion, combined with the very widely differing physical and chemical properties of the vegetable oils against those for the diesel fuel, aid to the correct interpretation of the observed engine behavior.     

Combustion and emission characteristics of DME as an alternative fuel for compression ignition engines with a high pressure injection system

The subject of this work is the investigation of the injection characteristics of neat dimethyl ether (DME) and the effect of DME fuel on the exhaust emission characteristics and engine performance of compression ignition engines. In order to analyze the injection characteristics of DME fuel as an alternative fuel for compression ignition engines, experiments were conducted to obtain the injection rate profile. The effective nozzle diameter and its velocity, and the discharge coefficient of the nozzle were analyzed by applying a nozzle flow model that accounted for the effect of cavitation. In addition, combustion characteristics of DME and diesel fuel in terms of combustion pressure, rate of heat release, indicated mean effective pressure (IMEP), and ignition delay at various injection timings were investigated on a constant energy input basis.When a constant pulse width was applied, the results of DME injection characterization showed that the actual injection duration of DME was longer than that of diesel fuel because the injection started faster and ended with more delay. The DME fueled engine showed slightly higher IMEP and NO_x emission with drastically lower CO and HC emissions and the possible reasons for the higher IMEP of DME fuel was discussed.     

Some physical properties and oxidative stability of biodiesel produced from oil seed crops

Biodiesel is a cleaner burning fuel than petrodiesel and a suitable replacement in diesel engine. It is produced from renewable sources such as vegetable oils or animal fats. Biodiesel fuel was prepared from castor (CSO), palm kernel (PKO) and groundnut (GNO) oils through alkali transesterification reaction. The biodiesel produced was characterized as alternative diesel fuel. Fuel properties such as specific gravity, viscosity, calorific (combustion) value, The CSO, PKO and GNO were measured to evaluate the storage/oxidative stability of the oils to compare them with commercial petrodiesel. The biodiesel produced had good fuel properties with respect to ASTM D 6751 and EN 14214 specification standards, except that the kinematic viscosity of castor oil biodiesel was too low. The viscosity of castor oil biodiesel at different temperatures was in the range of 4.12–7.21 mm²/s. However, promising results which conformed to the above specification standards were realized when castor oil biodiesel was blended with commercial petrodiesel. At 28 °C the specific gravity recorded for CSO, PKO and GNO biodiesel was higher than the values obtained for petrodiesel. Commercial petrodiesel had the highest oxidative stability than biodiesel produced from CSO, PKO and GNO oils.     

Biodiesel combustion in an optical HSDI diesel engine under low load premixed combustion conditions

An optically accessible single-cylinder high-speed direct-injection (HSDI) diesel engine was used to investigate the spray and combustion processes for biodiesel blends under different injection strategies. The experimental results indicated that the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation. The ignition and heat release rate peak occurred later with increasing biodiesel content. Fuel impingement on the wall was observed for all test conditions. The liquid penetration became longer and the fuel impingement was stronger with the increase of biodiesel content. Early and late injection timings result in lower flame luminosity due to improved mixing with longer ignition delay. For all the injection timings, lower soot luminosity was seen for biodiesel blends than pure diesel fuel. Furthermore, NO_x emissions were dramatically reduced for premixed combustion mode with retarded post-TDC injection strategies.     

Emission Reduction of Regenerative Fuel Powered Co-Generation Plants with SCR- and Oxidation-Catalysts

Since the beginning of combustion engine development in this recent century various different fuels have been successfully tested. Diesel engines have been adapted to fuels made from mineral oils because of the rising importance and the cheapness in comparison to other fuels. On the other hand, it is possible to burn regenerative fuels in engines and achieve some significant advantages in comparison to fossil diesel fuel. This is, for example, a closed carbon dioxide (CO₂) cycle which causes no green house effect. It is possible to extract oil from various seeds like rapeseed. It is also possible to burn used oil from the food processing industry or waste grease and oil from food recycling companies. The great advantages: (1) food recycling oils can produce energy instead of use as animal food, and (2) as nobody knows exactly the consistency of the collected oils, poisonous pollution is possible. These regenerative fuels can be burned without any further processing in special adapted diesel engines, for example an Elsbett engine, or in precombustion engines with large swept volumes. Most researchers focused on operating diesel engines with regenerative fuels and reducing the emissions caring only about regulated exhaust components. In comparison to these studies it is necessary to learn more about the emissions beyond the exhaust regulations. Additionally emission reduction is possible by using an SCR-catalyst (selective catalytic reduction) to reduce the NO₂ combined with an oxidation-catalyst which reduces any kind of oxidisable emissions. The TU München, Lehrstuhl für Energie- und Umwelttechnik der Lebensmittelindustrie, operates a small co-generation plant with the ability of analysing the standard emission components (CO, NO₂, HC, particles, CO₂, O₂) and unregulated components (SO₂, NH₃, polycyclic aromatic hydrocarbons (PAH), aldehyde, ketone). The emissions show some significant differences in comparison to fossil diesel fuel which is caused by the diversity of each fuel. Results of an investigation on four different fuels (wastefat methyl ester (WME), rapeseed methyl ester (RME), rapeseed oil and diesel fuel) burned in a small co-generation plant with a SCR- and oxidation-catalyst will be presented. A comparison to the emissions before and after the catalysts will be shown additionally to the results of the different reduction potential of diesel fuel, methyl ester or untreated oils. The combination of regenerative fuel and catalyst shows good potential for reducing the emissions. Furthermore the use of regenerative fuels is a sustainable production of energy with an overall efficiency of almost 90%. Regenerative fuels based on vegetable oils and waste fat are a valuable form of energy and have some significant advantages in comparison to diesel fuel, like an almost closed carbon dioxide cycle, rapid biological decomposition and lower CO, HC and particle emissions. Regenerative fuels should also meet minimum standards discussed in the paper to avoid the risk of engine damage and to reduce emissions.