Application potential of vegetable oils as alternative to diesel fuels in compression ignition engines: A review

Vegetable oils have been identified as the promising alternative source to replace fossil based fuel in the compression ignition (CI) engine. It is renewable and possesses characteristics that is similar to that of the diesel. Biodiesel, transesterifiedform of vegetable oil (VO), is now being commercially used in CI engines. However, biodiesel production from VO involves use of alcohols and chemicals which results the need of skilled labor and investment for its production. In view of this, many studies are also being carried out on the direct use of VO in the engine. The direct use of VO oil in engine is as good as that of the diesel. The superior quality of diesel however makes it better performance in engine as compared to the vegetable oil. Preheating and blending of VO are found to be the most common solution to overcome its inferior properties. The use of preheated and blended VO is found to improve the engine overall performance. This paper is focused exclusively on the one-to-one basis of study pertaining to the effect of neat, preheated and blended vegetable oils on diesel engine performance and emission through supplementation of illustrative figures from the various experimental studies.     

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。     

NOX emissions of compression ignition engines fueled with various biodiesel blends: A review

There are some challenges about NO_X emissions exhausted from diesel engines fueled with biodiesel. Due to increasingly stringent emission regulations, the different methods such as varying the engine operating parameters, treatment with antioxidant additive and blending fuels have been adapted to reduce emissions of biodiesel combustion. One of the effective methods is the combustion of dual or blending fuels. Various fuels such as gasoline, hydrogen, natural gas, biogas, different types of alcohols and also fuel additives have been used to reduce biodiesel disadvantages. This study reviews the potential of the different fuels as an additive in biodiesel fuel in correspond to reduce NO_X emissions. The general reduction of NO_X has been observed with the presence of gasoline, biogas and alcohols in biodiesel blends. The reduction of NO_X in biodiesel-hydrogen, biodiesel-diesel or biodiesel–CNG combustion has not been observed through all engine conditions. Moreover the retarding injection timing, the lower injection pressure, EGR higher than 30% can result in the reduced NO_X emissions. However it seems the decrease in NO_X emissions can be achieved by the use of most fuels in blending with biodiesel under all engine operating conditions, if only the proper injection parameters and blending proportions of fuels are set.     

A study of hydrogen fuelled compression ignition engines

The possibility of establishing a hydrogen fuelled compression ignition engine has been investigated experimentally using a conventional swirl chamber diesel engine. Two different attempts are included in this work; one dealing with the compression ignition on an air-aspirated engine system, and another with an engine operating with an argon-oxygen charge. In the former, the effect of preliminary fuelling was clarified in detail. It has been suggested that both pilot injection and fuel leakage from the injector can aid ignition of the hydrogen fuel, bringing about a smooth operation. A discussion is given of the mechanism of stabilizing ignition, from the viewpoint of thermal interactions between the engine cycles. In the latter attempt, a closed-cycle engine system is oriented and has been simulated by supplying a 21% oxygen containing mixture to the test engine. The result has indicated that ignition and engine operation are satisfactory without any ignition aid. A considerable gain has also been proved in thermal efficiency of using the argon mixture. Also, the practical feasibility of a closed-cycle compression ignition engine has been discussed.     

Future fuels and mixture preparation methods for spark ignition automobile engines

Research in the automobile industry focuses on studies of spark ignition automobile engines especially of stratified charge engines, lean combustion concepts, engines fueled by alcohol/gasoline blends, alcohol engines, and engines with on-board gas generators fueled by a variety of liquid fuels. The goal of this work is the development of low-emission, high fuel-economy and high performance power systems for the early 1990s. The implementation of this objective makes it necessary for more information on future fuel characteristics. In addition proper mixture preparation methods must be applied to find solutions to specific problems such as NO_x formation and aldehyde emission, while maintaining good fuel economy and high engine efficiency. The goal of this paper is to discuss the most attractive approaches for improved preparation and distribution of the fuel-air mixture with respect to future fuels such as alcohol/gasoline blends and other alcohol fuels.     

Automotive engines and fuels: A review of future options

This paper reviews the current status and development potential of automotive heat engines: various types of internal combustion engines, the gas turbine, Stirling and Rankine cycle engines, and compound engine systems. Expected changes in transportation fuels from natural petroleum, and the likely impact of alternative fuels are also examined. Emphasis is placed on the general structure of the issues to be faced in making choices about where to put research and development resources, rather than on technical detail, to provide an overview of this broad area.     

Using renewable alternative fuels and studying their impact on the performance and emissions of compression ignition engines

This practical study examined the effect of engine torque on engine performance and emissions. The most important parameters of engine performance are thermal efficiency, brake power (BP), and specific fuel consumption. As for exhaust emissions, the most important of which are hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (NO_x). The experiment was conducted for a single-cylinder, four-stroke compression ignition engine. Mixtures (B0, B10, B20, B30, and B40) were taken from biodiesel prepared from sunflower oil by the esterification method. The engine speed was fixed at 1700 rpm, and torque variable was from 0 to 10 N m. The results indicated a decrease in engine BP by an average of 19.5 W, a decrease in thermal efficiency by an average of 1.058%, while an increase in fuel consumption by an average of 0.095 kg/kW h⁻¹ compared to diesel. As for exhaust emissions, HC emissions decreased by 5.8 ppm, while CO decreased by 0.0207%, and NO_x emissions increased by 138.5 ppm compared to diesel, due to changes in the properties of biodiesel, such as high density, viscosity, and low calorific value compared to the properties of regular diesel     

Transesterified Hingan (Balanites) oil as a fuel for compression ignition engines

The study endeavor to utilize esters of Balanites aegyptiaca (L.) Del(Balanites) as a fuel for diesel engine. Ester developed from balanites oil by the transesterification process is investigated for its properties and the engine performance. A single stage alkali-catalyzed esterification process by using 1.25% KOH, methyl alcohol 8:1 molar ratio with respect to balanites oil, gives the maximum ester yield of 95%. The performance and emission characteristics of the engine are analyzed using balanites oil methyl esters and diesel as fuel. The viscosity of balanites oil is found to be decreased by 89% after esterification, and the calorific value of balanites oil methyl esters is nearly 94% of the diesel fuel. The engine performance with balanites oil methyl ester as a fuel resembles to that of conventional diesel fuel, while the exhaust gas emissions are reduced with the use of balanites oil methyl esters.     

A review of hydrogen as a compression ignition engine fuel

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. This fact, combined with the recent diesel emission scandal and the rumours of more widespread cheating by automotive manufacturers have initiated a long discussion about the future and sustainability of diesel engines.Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high-efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency.This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines. A comprehensive review of the past and recent research activities on the topic is documented. The review focuses on the in-cylinder combustion of hydrogen either as a primary fuel or in dual fuel operation. The effects of injection strategies, compression ratio and exhaust gas recirculation on the combustion and emission characteristics of the hydrogen fuelled engine are fully analysed. The main limitations, challenges and perspectives are presented.     

A review of ammonia as a compression ignition engine fuel

During the past decades, the diesel engine has been through times of upheaval, boom and bust. At the beginning of the century, almost 50% of the new vehicle registrations in the European market were diesel-powered. However, the news of deadly diesel NO_x emissions supported by the diesel emission scandals caused a shock to the diesel engine market, and the sustainability of the diesel engine is currently in dispute.Recently major automotive manufacturers announced the development of diesel-powered vehicles with negligible NO_x emissions. Moreover, the NO_x emissions production is of lower concern for heavy-duty, marine or power generations applications where the implementation of advanced aftertreatment systems is feasible. However, despite the tackle of NO_x emissions, the decarbonisation of the automotive, marine and power generation markets is mandatory for meeting greenhouse gas emissions targets and limiting global warming.The decarbonisation of the diesel engine can be achieved by the implementation of a carbon-free fuel such as ammonia. This paper provides a detailed overview of ammonia as a fuel for compression ignition engines. Ammonia can be combusted with diesel or any other lower autoignition temperature fuel in dual-fuel mode and lead to a significant reduction of carbon-based emissions. The development of advanced injection strategies can contribute to enhanced performance and overall emissions improvement. However, ammonia dual-fuel combustion currently suffers from relatively high unburned ammonia and NO_x emissions because of the fuel-bound nitrogen. Therefore, the implementation of aftertreatment systems is required. Hence, ammonia as a compression ignition fuel can be currently seen as a feasible solution only for marine, power generation and possibly heavy-duty applications where no significant space constraints exist.     

Hydrogen dual-fuelling of compression ignition engines with emulsified biodiesel as pilot fuel

Dual-fuel compression ignition (CI) engine operation with hydrogen is a promising method of using hydrogen gas in CI engines via high-cetane pilot fuel ignition. However, hydrogen dual-fuel operation with neat pilot fuels typically produce: high NO_x emissions; and high combustion chamber pressure rise rates (leading to increased “Diesel knock” tendencies). While water-in-fuel emulsions have been used during normal CI engine operation to cool the charge and slow combustion rates in an effort to reduce NO_x emissions, these water-in-fuel emulsions have not been tested as pilot fuels during hydrogen dual-fuel combustion. In this work two water-in-biodiesel emulsions are tested as pilot fuels during hydrogen dual-fuel operation. Hydrogen dual-fuel operation generally produces at best comparable thermal efficiencies compared with normal CI engine operation, while the emulsified biodiesel pilot fuels generally increase thermal efficiencies when compared with the neat biodiesel pilot fuel during dual-fuel operation. There is also a clear reduction in NO_x emissions with emulsified pilot fuel use compared with the neat pilot fuel. The thermal efficiency increase is more apparent at higher engine speeds, while the NO_x reduction is more apparent at lower speeds. This is due to two conflicting effects (exclusive to emulsified pilot fuel) that occur in tandem. The first is the cooling effect of water vapourisation on the charge, while the second is the microexplosion phenomenon which enhances fuel-air mixing. The NO_x emission reduction is due to the emulsified pilot fuel lowering pressure rise rates compared with the neat pilot fuel, while the efficiency increase is due to a more homogeneous charge resulting from the violent microexplosion of the emulsified pilot fuel. Smoke, CO, HC and CO₂ emissions remain comparable to neat pilot fuel tests. Overall, emulsified pilot fuels can reduce NO_x emissions and increase thermal efficiencies, however not at the same instance and under different operating conditions. The general trends of reduced power output, reduced CO₂ and increased water vapour emission during hydrogen dual-fuel operation (with neat pilot fuels) are also maintained.     

Vegetable oils as renewable fuels for power plants based on low and medium speed diesel engines

There is a high potential for plant oils as alternative fuel for low and medium speed diesel engines, making petroleum-derived fuels likely to be replaced in these types of engines. Vegetable oils have important advantages over both heavy fuel oil (HFO) and marine gas oil (MGO), the fuels currently used in diesel power plants by large two stroke low-speed diesel engines and by medium speed diesel engines, respectively. The emission of certain pollutants and greenhouse gases like SO_x, soot and, mainly, CO₂ can be reduced by using vegetable oils in these types of engines. This work discusses the potential of vegetable oils as fuel for power plant diesel engines and the problems that can be derived from their use. Current experiences with medium speed diesel engines together with the analysis carried out in this paper indicate that vegetable oils can substitute HFO and MGO, without almost any engine modification.     

Characterization and effect of using rubber seed oil as fuel in the compression ignition engines

Vegetable oils pose some problems when subjected to prolonged usage in compression ignition engines because of their high viscosity and low volatility. The common problems are poor atomization, carbon deposits, ring sticking, fuel pump failure, etc. Converting the high viscosity vegetable oil into its blends or esters can minimize these problems. The various blends of rubber seed oil and diesel were prepared and its important properties such as viscosity, calorific value, flash point, fire point, etc. were evaluated and compared with that of diesel. The blends were then subjected to engine performance and emission tests and compared with that for diesel. It was found that 50–80% of rubber seed oil blends gave the best performance. Long run tests were conducted using optimized blend and diesel. It was found that blend fueled engine has higher carbon deposits inside combustion chamber than diesel-fueled engine. Utilization of blends requires frequent cleaning of fuel filter, pump and the combustion chamber. Hence, it is recommended that rubber seed oil–diesel blend fuel is more suitable for rural power generation.     

Progress and recent trends in homogeneous charge compression ignition (HCCI) engines

HCCI combustion has been drawing the considerable attention due to high efficiency and lower nitrogen oxide (NO_x) and particulate matter (PM) emissions. However, there are still tough challenges in the successful operation of HCCI engines, such as controlling the combustion phasing, extending the operating range, and high unburned hydrocarbon and CO emissions. Massive research throughout the world has led to great progress in the control of HCCI combustion. The first thing paid attention to is that a great deal of fundamental theoretical research has been carried out. First, numerical simulation has become a good observation and a powerful tool to investigate HCCI and to develop control strategies for HCCI because of its greater flexibility and lower cost compared with engine experiments. Five types of models applied to HCCI engine modelling are discussed in the present paper. Second, HCCI can be applied to a variety of fuel types. Combustion phasing and operation range can be controlled by the modification of fuel characteristics. Third, it has been realized that advanced control strategies of fuel/air mixture are more important than simple homogeneous charge in the process of the controlling of HCCI combustion processes. The stratification strategy has the potential to extend the HCCI operation range to higher loads, and low temperature combustion (LTC) diluted by exhaust gas recirculation (EGR) has the potential to extend the operation range to high loads; even to full loads, for diesel engines. Fourth, optical diagnostics has been applied widely to reveal in-cylinder combustion processes. In addition, the key to diesel-fuelled HCCI combustion control is mixture preparation, while EGR is the main path to achieve gasoline-fuelled HCCI combustion. Specific strategies for diesel-fuelled, gasoline-fuelled and other alternative fuelled HCCI combustion are also discussed in the present paper.     

Effects of primary breakup modeling on spray and combustion characteristics of compression ignition engines

Injector flow dynamics and primary breakup processes are known to play a pivotal role in determining combustion and emissions in diesel engines. In the present study, we examine the effects of primary breakup modeling on the spray and combustion characteristics under diesel engine conditions. The commonly used KH model, which considers the aerodynamically induced breakup based on the Kelvin-Helmholtz instability, is modified to include the effects of cavitation and turbulence generated inside the injector. The KH model and the new (KH-ACT) model are extensively evaluated by performing 3-D time-dependent simulations with detailed chemistry under diesel engine conditions. Results indicate that the inclusion of cavitation and turbulence enhances primary breakup, leading to smaller droplet sizes, decrease in liquid penetration, and increase in the radial dispersion of spray. Predictions are compared with measurements for non-evaporating and evaporating sprays, as well as with flame measurements. While both the models are able to reproduce the experimentally observed global spray and combustion characteristics, predictions using the KH-ACT model exhibit closer agreement with measurements in terms of liquid penetration, cone angle, spray axial velocity, and liquid mass distribution for non-evaporating sprays. Similarly, the KH-ACT model leads to better agreement with respect to the liquid length and vapor penetration distance for evaporating sprays, and with respect to the flame lift-off location for combusting sprays. The improved agreement is attributed to the ability of the new model to account for the effects of turbulence and cavitation generated inside the injector, which enhance the primary breakup. Results further indicate that the combustion under diesel engine conditions is characterized by a double-flame structure with a rich premixed reaction zone near the flame stabilization region and a non-premixed reaction zone further downstream. This flame structure is consistent with the Dec’s model for diesel engine combustion (Dec, 1997) [1], and well captured by a newly developed flame index based on the scalar product of CO and O₂ mass fraction gradients.     

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.     

A novel compression strategy for air hybrid engines

A novel compression strategy for air hybrid engines is proposed utilizing two storage tanks which increases the efficiency of regenerative braking of air hybrid vehicles significantly by increasing the stored air mass and, consequently, the storing pressure in the tank. The second law definition for efficiency is suggested and employed to evaluate the regenerative system capability in storing the kinetic energy of a decelerating vehicle. The maximum energy storing capacity of conventional and proposed compression methods are derived and the advantage of the double-tank system in increasing the energy storing capacity is shown. An experimental setup has also been designed and tested to evaluate the double-tank compression strategy in practice. The experimental results show at least 70% improvement in storing pressure and 125% improvement in energy storing capability in the regenerative braking process using the double-storage system.     

Diethyl ether as an ignition improver for acetylene-fuelled homogeneous charge compression ignition operation: an experimental investigation

In this study, a single-cylinder, water-cooled, direct-injection, compression ignition (CI) engine is operated on the homogeneous charge CI (HCCI) mode using acetylene and diethyl ether (DEE) as fuels. Acetylene is inducted as a main fuel and a small quantity of DEE is injected into the intake manifold for controlling combustion phasing. The engine performance and exhaust emission characteristics are investigated experimentally under various operating conditions. From the results, it is found that brake thermal efficiency of the acetylene-DEE HCCI mode is comparable with that of the conventional CI mode. It has a wide operating range of 0–4.2 bar brake mean effective pressure without exhaust gas recirculation compared with the liquid fuels-HCCI mode. The engine could easily start in the HCCI mode using DEE alone. Nitric oxide and smoke emissions are at ultra-low level. Hydrocarbon emissions are comparatively lower at lower loads and higher at higher load conditions. Carbon monoxide emissions are comparable with that of the conventional CI mode.     

A multi-mode combustion diagram for spark assisted compression ignition

The potential utility of spark discharges to assist low temperature, compression ignited engines has resulted in a number of experimental studies. These show mixed results; sometimes spark is effective at controlling heat release timing, sometimes it only stabilizes combustion, and sometimes it has no effect at all. In order to help understand the spark assisted process we propose a multi-mode combustion diagram to delineate the regimes of spark ignition, flame propagation, compression ignition, knocking combustion and spark-assisted combustion, in terms of unburned and burned gas temperatures near top dead center. An analysis of existing experimental data suggests that the effectiveness of spark assist is best at higher and middle loads and decreases as load is reduced.     

Biodiesel,emulsified biodiesel and dimethyl ether as pilot fuels for natural gas fuelled engines

Dual-fuelling in compression–ignition (CI) engines is a mode of combustion where a small pilot injection of high-cetane fuel (i.e. diesel) ignites a premixed high-octane fuel (i.e. methane) and air mixture. This allows conventional CI engines to lower their emissions of smoke and nitrogen oxides (NO_x)$({\text{NO}}_x)$ while maintaining their high thermal efficiencies. However, poor ignitability of the main fuel–air charge results in increased emissions of unburnt hydrocarbons (HC) and carbon monoxide (CO). Conventional pilot fuels such as diesel and biodiesel (methyl esters transesterified from raw plant oil) have been researched extensively in prior work, showing that in terms of performance and emissions they perform fairly similarly. This is because the physical, chemical and combustion properties of various methyl esters are comparable to those of conventional diesel. In order to reduce these emissions of HC and CO, alternative pilot fuels need to be considered. As fuels employed during normal CI engine operation, both dimethyl ether (DME, a gaseous CI engine fuel) and water-in-fuel emulsions (conventional biodiesel mixed with varying concentrations of water) have shown that they reduce smoke and _NOx${\mathrm{NO}}_x$ emissions significantly, while improving combustion quality. In this work, the performance of DME and water-in-biodiesel emulsions as pilot fuels was assessed. It was seen that the water-in-biodiesel emulsions did not perform as well as expected, as increased HC and CO emissions coupled with a mild change in _NOx${\mathrm{NO}}_x$ levels was encountered (compared to conventional pilot fuel, in this case neat biodiesel). The emulsions performed very poorly as pilot fuels below a certain BMEP threshold. DME, while producing higher levels of HC and CO than neat biodiesel, managed to reduce _NOx${\mathrm{NO}}_x$ significantly compared to neat biodiesel. Emissions of HC and CO, while higher than neat biodiesel, were not as high as levels seen with the emulsions. Thermal efficiency levels were generally maintained with the liquid pilot fuels, with the DME pilot producing comparatively lower levels.