Nanomaterials as fuel additives in diesel engines: A review of current state,opportunities, and challenges

Nanomaterials exhibit excellent properties, allowing them to act as fuel additives to improve diesel engine characteristics. This review highlights the unique potentials of nanomaterials and their activities in diesel engines to achieve lower harmful diesel emissions and better engine performance. The effects of nanomaterial-enriched fuels on engine characteristics and engine subsystems as well as associated opportunities, identified from laboratory test results obtained in recent years, are discussed. On the basis of two criteria, the best nanomaterial-base fuel pairs are identified from the set of the most frequently tested nanomaterials engaged as fuel additives in diesel engines. This is followed by a review of technical challenges that will need to be addressed and resolved to assure practical viability of nanomaterials acting as fuel additives. Finally, the environmental and human health risks, exposed by investigations in recent years, are reviewed. Wherever possible, potential solutions to outstanding problems are addressed and discussed briefly.     

Combustion of fat and vegetable oil derived fuels in diesel engines

In this article, the status of fat and oil derived diesel fuels with respect to fuel properties, engine performance, and emissions is reviewed. The fuels considered are primarily the methyl esters of fatty acids derived from a variety of vegetable oils and animal fats, and referred to as biodiesel. The major obstacle to widespread use of biodiesel is the high cost relative to petroleum. Economics of biodiesel production are discussed, and it is concluded that the price of the feedstock fat or oil is the major factor determining biodiesel price.Biodiesel is completely miscible with petroleum diesel fuel, and is generally tested as a blend. The use of biodiesel in neat or blended form has no effect on the energy based engine fuel economy. The lubricity of these fuels is superior to conventional diesel, and this property is imparted to blends at levels above 20 vol%. Emissions of PM can be reduced dramatically through use of biodiesel in engines that are not high lube oil emitters. Emissions of NO_x increase significantly for both neat and blended fuels in both two- and four-stroke engines. The increase may be lower in newer, lower NO_x emitting four-strokes, but additional data are needed to confirm this conclusion. A discussion of available data on unregulated air toxins is presented, and it is concluded that definitive studies have yet to be performed in this area. A detailed discussion of important biodiesel properties and recommendations for future research is presented. Among the most important recommendations is the need for all future studies to employ biodiesel of well-known composition and purity, and to report detailed analyses. The purity levels necessary for achieving adequate engine endurance, compatibility with coatings and elastomers, cold flow properties, stability, and emissions performance must be better defined.     

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.     

二甲醚用作柴油机燃料的进展

介绍二甲醚作为柴油发动机燃料的进展 ,有关发动机的性能、微粒排放、燃料喷射、磨损和密封、着火延迟及安全性能问题     

Efficiencies of heat engines and fuel cells: The methanol fuel cell as a competitor to otto and diesel engines

As the real cost of fuel rises the efficiency of energy conversion devices will become of increasing importance. Efficiency is a variable factor depending inter alia on load factor. Whereas heat engines commonly yield optimum efficiencies at near to maximum power, fuel cells yield optimum efficiencies at zero power. Projections based on realistic developments suggest that fuel cells will operate overall with higher efficiencies than heat engines when load factors are below ～45%. Road transportation generally operates at load factors much lower than this and represents a suitable market for fuel cells.     

Use of vegetable oil as fuel to improve the efficiency of cooking stove

In this study, an attempt has been made to use waste vegetable oil as a fuel for a cooking stove. Suitable modifications have been made in the kerosene stove for use with vegetable oil as fuel. The efficiency of the stove using vegetable oil as fuel is observed to be as high as 48.9% as compared to 34.9% with that of a conventional stove when a flat copper bottom vessel is used. Corresponding efficiency increase is also observed with other vessels.     

An evaluation of the life cycle cost of rapeseed oil as a straight vegetable oil fuel to replace petroleum diesel in agriculture

The use of straight vegetable oil (SVO) as biofuel has been recognized as a valid substitute of diesel fuel in the agricultural sector under specific circumstances. Its direct use reduces most of the chemical processes involved when converting it into biodiesel, thus lowering harmful emissions. This study presents the economic analysis of a self-supply farming model that uses rapeseed as its fuel base. This model addresses agricultural environmental concerns and can even minimize dependence on the fluctuating costs of diesel fuel. The use of SVO in agriculture can help reduce farmers’ vulnerability to fossil fuel prices. The economic evaluation of the model proposed in this study shows clear economic benefits of introducing rapeseed to the traditional crop rotation of wheat and barley. The key factors analyzed in this model are diesel fuel price, diesel fuel grants and crop aids. The current situation in Spain favors the use of diesel fuel in agriculture rather than rapeseed SVO due to an 8% profit difference. However, results show that changes in key factors slightly affect the profit margin, calculating a difference of only 3.7% for particular factor combinations. Combined environmental-friendly agriculture supporting policies are necessary to cover this slight profit difference to promote this biofuel.     

Comparative performance and emission studies when using olive oil as a fuel supplement in DI and IDI diesel engines

An experimental study is conducted to evaluate and compare the use of a diesel fuel supplement, specifically a 25/75% and a 50/50% blend of waste olive oil and commercial diesel fuel, in a four-stroke, DI (Direct Injection) diesel engine and in a four-stroke, IDI (Indirect Injection) diesel engine having a swirl-combustion chamber. The influence of the blends (diesel fuel+olive oil), for a large range of loads, has been examined on fuel consumption, maximum pressure, exhaust temperature, exhaust smokiness and exhaust-gas emissions such as nitrogen oxides (NO_x), hydrocarbons (HC) and carbon monoxide (CO). The differences in the measured performance and exhaust-emission parameters, from the baseline operation of either engine, are determined and compared. The study shows, for both the DI and IDI engines, a small penalty in specific fuel consumption, a moderate increase in exhaust smokiness and essentially unaltered maximum pressures and exhaust temperatures when using the blends. Also, for both the IDI and DI engines when using the blends, the study shows moderate decreases in emitted nitrogen oxides and increases in hydrocarbons as well as negligible increases in emitted carbon monoxide. Theoretical aspects of diesel engine combustion are used to aid the interpretation of the observed engines' behaviour.     

Study on cottonseed oil as a partial substitute for diesel oil in fuel for single-cylinder diesel engine

The experiments were undertaken to obtain the knowledge necessary for raising the thermal efficiency of mixed oil composed of cottonseed oil and conventional diesel oil and for improving the performance of engine fuelled by the mixture. The experimental results obtained showed that a mixing ratio of 30% cottonseed oil and 70% diesel oil was practically optimal in ensuring relatively high thermal efficiency of engine, as well as homogeneity and stability of the oil mixture. A quadratic regressive orthogonal design test method was adopted in the experiment designed to examine the relationship between specific fuel consumption and four adjustable working parameters (intake-valve-closing angle (α), exhaust-valve-opening angle (β), fuel-delivery angle (θ) and injection pressure (P, in 10⁴ Pa)) when the above-mentioned oil mixture was used. The mathematical equations characterizing the relationship were formulated. The equation of specific fuel consumption derived from the regressive test under each operating condition was set as the objective function and the ranges for the four adjustable working parameters were the given constraint condition. Models of non-linear programming were then constructed. Computer-aided optimization of the working parameters for 30:70 cottonseed oil/diesel oil mixed fuel was achieved. It was concluded that the predominant factor affecting the specific fuel consumption was fuel-delivery angle θ, the approximate optimal value of which, in this specific case, was 3–5° in advance of that for engine fuelled by pure diesel oil. The experimental results also provided useful reference material for selection of the most preferable combination of working parameters.     

Well-to-Tank environmental analysis of a renewable diesel fuel from vegetable oil through co-processing in a hydrotreatment unit

A Life Cycle Assessment (LCA) study of HidroBioDiésel (HBD) was carried out. This partly renewable diesel fuel is obtained from the co-processing of soybean vegetable oil with conventional fossil fuel in hydrotreating facilities of crude oil refineries. The environmental profile of HBD was assessed for the fossil energy use and climate change impact categories. The production systems of equivalent fuels -blends of Fatty Acid Methyl Ester (FAME, a biofuel obtained by means of transesterification of vegetable oil) and mineral diesel with sulphur content below 10 ppm were also assessed for comparison purposes. The environmental performance of HBD systems compares favourably to those of FAME and diesel blends for the selected impact categories. The estimated environmental benefits of HBD (assuming a 13% renewable blend) include reductions of up to 2% in fossil energy use and 9% in climate change impacts.     

谈柴油车的节油技术

针对柴油车的节油技术，本文结合柴油车的使用环境，从驾驶，维护及柴油机自身结构等方面作了几点探讨。     

Use of hydrogen in dual-fuel diesel engines

Hydrogen is a promising future energy carrier due to its potential for production from renewable resources. It can be used in existing compression ignition diesel engines in a dual-fuel mode with little modification. Hydrogen's unique physiochemical properties, such as higher calorific value, flame speed, and diffusivity in air, can effectively improve the performance and combustion characteristics of diesel engines. As a carbon-free fuel, hydrogen can also mitigate harmful emissions from diesel engines, including carbon monoxide, unburned hydrocarbons, particulate matter, soot, and smoke. However, hydrogen-fueled diesel engines suffer from knocking combustion and higher nitrogen oxide emissions. This paper comprehensively reviews the effects of hydrogen or hydrogen-containing gaseous fuels (i.e., syngas and hydroxy gas) on the behavior of dual-fuel diesel engines. The opportunities and limitations of using hydrogen in diesel engines are discussed thoroughly. It is not possible for hydrogen to improve all the performance indicators and exhaust emissions of diesel engines simultaneously. However, reformulating pilot fuel by additives, blending hydrogen with other gaseous fuels, adjusting engine parameters, optimizing operating conditions, modifying engine structure, using hydroxy gas, and employing exhaust gas catalysts could pave the way for realizing safe, efficient, and economical hydrogen-fueled diesel engines. Future work should focus on preventing knocking combustion and nitrogen oxide emissions in hydrogen-fueled diesel engines by adjusting the hydrogen inclusion rate in real time.     

The use of hazelnut oil as a fuel in pre-chamber diesel engine

This paper briefly reviews the use of hazelnut oil as an alternative fuel in pre-chamber diesel engines, and compares it with diesel fuel. In order to investigate the effects of the use of hazelnut oil as a diesel engine fuel, an experimental setup was constructed. The results showed that the hazelnut oil may be employed as a possible candidate for most diesel fuel operating conditions in terms of the performance and emission parameters without any modification and preheating of the fuels.     

Performance analysis of a mono-cylinder diesel engine using soy straight vegetable oil as fuel with varying temperature and injection angle

Experimental results are presented for a compression ignition engine with one cylinder refrigerated by air, fueled with soy straight vegetable oil (SVO), filtered at 500 nm and blended with diesel at volume percentages of 10, 30, 50, 70 and 100%. Performance tests varying the injection angle and the fuel temperature were conducted. The results show an increase in torque and power compared to pure diesel, especially with the SVO50 and SVO70 mixtures. However, there was an increase in the specific consumption, although engine efficiency was only slightly lower due to the lower heating value of oil. The use of SVO as fuel is feasible, but durability tests must be performed, mainly to discover potential maintenance problems.     

Biodiesel fuel in diesel micro-turbine engines: Modelling and experimental evaluation

Many performance and emission tests have been carried out in reciprocating diesel engines that use biodiesel fuel over the past years and very few in gas turbine engines. This work aims at assessing the thermal performance and emissions at full and partial loads of a 30 kW diesel micro-turbine engine fed with diesel, biodiesel and their blends as fuel. A cycle simulation was performed using the Gate Cycle GE Enter software to evaluate the thermal performance of the 30 kW micro-turbine engine. Performance and emission tests were carried out on a 30 kW diesel micro-turbine engine installed in the NEST laboratories of the Federal University of Itajubá, and the performance results were compared with those of the simulation. There was a good agreement between the simulations and the experimental results from the full load down to about 50% of the load for diesel, biodiesel and their blends. The biodiesel and its blends used as fuel in micro-turbines led to no significant changes in the engine performance and behaviour compared to diesel fuel. The exhaust emissions were evaluated for pure biodiesel and its blends and conventional diesel. The results revealed that the use of biodiesel resulted in a slightly higher CO, lower NO_x and no SO₂ emissions.     

Comparative performance and emission studies for vaporized diesel fuel and gasoline as supplements in swirl-chamber diesel engines

An experimental study has been conducted to evaluate and compare the use of fumigated diesel fuel or gasoline as supplementary fuels for a naturally-aspirated, four-stroke diesel engine with a swirl-combustion chamber. The supplementary diesel fuel or gasoline is introduced together with the aspirated air (fumigation) in various proportions with respect to the main diesel fuel, which is injected in the usual manner. The influence of fuel/feed ratios (supplementary or main feed), for a large range of loads, has been examined on fuel consumption, pressure diagrams, exhaust smokiness and exhaustgas emissions (nitrogen oxides, hydrocarbons and carbon monoxide). Knocking limits have been determined. The differences in the measured performance and exhaust-emission parameters from baseline engine operation, when using either supplementary diesel fuel or gasoline fumigated in the intake air, are determined and compared. Our study shows promise for this approach and indicates that above ˜60% of maximum load, there is high smoke reduction with only a slight change in specific fuel consumption, when using either one of the supplementary fumigated fuels. Examination of gaseous pollutant levels shows involved relations with respect to load and fuel proportions. Theoretical aspects of the supplementary fuel-mode (fumigation) of combustion are used to explain the observed engine behaviour.     

Using of cotton oil soapstock biodiesel–diesel fuel blends as an alternative diesel fuel

In this study, usability of cotton oil soapstock biodiesel–diesel fuel blends as an alternative fuel for diesel engines were studied. Biodiesel was produced by reacting cotton oil soapstock with methyl alcohol at determined optimum condition. The cotton oil biodiesel–diesel fuel blends were tested in a single cylinder direct injection diesel engine. Engine performances and smoke value were measured at full load condition. Torque and power output of the engine with cotton oil soapstock biodiesel–diesel fuel blends decreased by 5.8% and 6.2%, respectively. Specific fuel consumption of engine with cotton oil soapstock–diesel fuel blends increased up to 10.5%. At maximum torque speeds, smoke level of engine with blend fuels decreased up to 46.6%, depending on the amount of biodiesel. These results were compared with diesel fuel values.     

Dual fuel mode operation in diesel engines using renewable fuels: Rubber seed oil and coir-pith producer gas

Partial combustion of biomass in the gasifier generates producer gas that can be used as supplementary or sole fuel for internal combustion engines. Dual fuel mode operation using coir-pith derived producer gas and rubber seed oil as pilot fuel was analyzed for various producer gas–air flow ratios and at different load conditions. The engine is experimentally optimized with respect to maximum pilot fuel savings in the dual fuel mode operation. The performance and emission characteristics of the dual fuel engine are compared with that of diesel engine at different load conditions. Specific energy consumption in the dual-fuel mode of operation with oil-coir-pith operation is found to be in the higher side at all load conditions. Exhaust emission was found to be higher in the case of dual fuel mode of operation as compared to neat diesel/oil operation. Engine performance characteristics are inferior in fully renewable fueled engine operation but it suitable for stationary engine application, particularly power generation.     

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.