Keywords

1 Introduction

German Thermal Engineer Rudolf C. Karl Diesel invented diesel engine in 1890s. At first, Dr. Diesel used peanut oil as fuel and in 1900, the inventor presented it at the Global Exhibition in Paris. The basic idea of Rudolf Diesel was to utilize fuel produced via biomass as a potential fuel for the engine. The inventor wanted to give an easy way for farmers to produce their fuel. R. Diesel said that “diesel engines can be run on edible and non-edible crop oil and would help substantially in the growth of various countries”. In 1912 Diesel stated, “The application of vegetable oil may seem to be unimportant today but such oils may prove to be as essential as present-day products of coal tar and petroleum”. Several factors such as biodegradability, availability, low sulphur content and renewability make vegetable oils suitable to be utilized as a fuel. In the early 1920s, manufacturers of the diesel engine used fossil fuels because of its lower viscosity instead of applying vegetable oil by simpler modifications, which resulted in an increase in pollution and huge depletion of fossil fuels. Later in the 1990s, due to its low polluting capabilities and its benefits biodiesel was accepted worldwide and many countries consider biodiesel as an important topic (Biodiesel Analytical Methods: August 2002–January 2004, 2004). The Philippines Government, in 2004, made it mandatory to add 1% of coconut biodiesel by volume to diesel fuel. Brazil, the world's leading producer and exporter of soybean, in 2004, passed a bill making it mandatory to yield 2% biodiesel fuel blend, consisting of soya oil and castor oil increasing it to 5% by 2013. The biggest manufacturer of biodiesel, the USA and Brazil, in 2016, produced up to 3–5 billion litres of biodiesel. To facilitate the sustainable development of a nation and to satiate the growing need for energy, it is crucial to have alternative fuels or energy resources. The energy crisis is a global issue challenging us which needs to be tended to as soon as possible. The current sources of non-renewable energy, i.e. fossil fuels are contributing largely to atmospheric pollution and greenhouse gases. Also, the conventional diesel fuel is a major source of harmful emissions like SOx, NOx, COx, HC, etc. Fossil fuels are speculated to be consumed in 65 more years. Most countries are experiencing international pressure on global warming issues [1]. Hence, for future purpose, countries are giving importance to renewable and clean alternative fuels. Biodiesel has seemed to be the most suitable alternative for diesel fuel since it possesses similar properties that of conventional diesel. Being biodegradable and eco-friendly, it can easily be used in various CI engines with or without little modification [2]. Reasons listed below show why biodiesel is growing in popularity as a substitute fuel:

  1. 1.

    Biodiesel exhaust emissions are non-toxic and non-polluting.

  2. 2.

    Commercialization of biodiesel will help the nation to be self-sufficient and energy independent.

  3. 3.

    Reduces and rectifies the long term effects caused by toxic emissions like smogs, acid rains, global warming, etc.

Biodiesel can be extracted from biological resources such as edible and non-edible vegetable crop oils or animal fat through transesterification process. Pure biodiesel cannot be directly used in diesel engines, therefore, blends of biodiesel and conventional diesel are required to be prepared. Jatropha oil biodiesel is suited for use in diesel engines provided that its flash point, cloud point, kinematic viscosity, and cetane number meet the recommended international standards. Jatropha biodiesel by itself is too viscous to be used as a diesel substitute. Blending ratio up to 45–50% of diesel with Jatropha is however found to be applicable [3].

2 Sources of Biodiesel

Biodiesel can be manufactured from sources like edible and non-edible vegetable crop oils, animal fats, soap sock and also from waste cooking oils. Biodiesel production in various countries is shown in Table 1.

Table 1 Details of biodiesel production in diverse countries [4]
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2.1 Production of Biodiesel

Biodiesel is produced from biomass. This conversion involves diverse chemical reactions like transesterification, catalytic cracking/pyrolysis, saponification, etc. Biomass includes edible and non-edible vegetable crop oils or animal fats reacted with chains of alcohols mainly methanol or ethanol. Because of lower molecular weight and low cost of ethanol, it is widely used for the manufacturing biodiesel. However, methanol is also an effective replacement for diesel. Both acid or base catalyst scan be used for increasing the rate of reaction but the most effective means of production is transesterification involving base catalyst. This method results in lower catalyst cost and lower reaction time than those with acid catalysis.

2.2 Edible and Non-edible Sources

The edible oils include rapeseed oil, corn oil, palm oil, coconut oil, sunflower oil, etc., whereas the non-edible oils include castor oil (Ricinus communis), neem oil, jatropha oil (Jatropha curcas) and almond oil, found to be appropriate for biodiesel production satisfying the experimental feasibility. Algae are considered as a substantial source for manufacturing biodiesel as well and have 200 times yielding capacity of biodiesel than that of vegetable oils (Table 2).

Table 2 Properties of different edible and non-edible oils
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Edible oil biodiesel with ethanol along with NaOH and Rhizopus oryzae lipase facilitate transesterification process, such as palm oil biodiesel, castor oil biodiesel and sunflower oil biodiesel, yielding 25.64 ml, 31.11 ml and 20.219 ml, respectively. This results in the production of smaller quantities of biodiesel such as POB, GOB, COB and SOB, i.e. 21.84 ml, 28.3 ml, 21.39 ml and 17.05 ml, respectively (production of biodiesel from edible and non-edible oils using Rhizopus oryzae and Aspergillus niger 2013).

2.3 Production of Biodiesel from Castor Oil

In this method, transesterification process involves specific treatment in which the raw vegetable oil gets converted into biodiesel, which is fatty acid alkyl ester. Transesterification is the best technique for manufacturing biodiesel fuel. A higher quantity of free fatty acids (FFA) (>1% w/w) leads to the formation of soap with alkaline catalyst and further results in separation of the biodiesel from the glycerin fraction. The amount of FFA is about 30% in crude oil which is far beyond the 1% level. Researchers have found many other ways for manufacturing biodiesel which contain a higher amount of FFA including—pretreatment step to reduce the free fatty acids of various feedstocks before the transesterification reaction completion. Reduction in FFA to < 1% can easily be obtained if esterification is followed by transesterification. Properties of castor oil as follows, density, FFA(%), Fire Point (°C), Fire Point (°C), Fire Point (°C), Fire Point (°C), Specific gravity and Calorific Value are 963, 0.0263, 335, 296, 15.8, 0.963, 35, 684.5.

2.4 Transesterification Process

Transesterification also termed as alcoholysis, it is the method of substituting the alkoxy group of an ester compounded by one more alcohol. It is a reversible process in which ester is transformed from one to another. Suitable alcohols comprise of mainly methanol and ethanol, also butanol, propanol and amyl alcohol. This process is usually used to decrease the viscosity of triglycerides, thus improving the engine performance and improving the chemical and physical characteristics of biofuel. Hence, fatty acid methyl ester (biodiesel) is obtained by transesterification.

2.5 Biodiesel Production from Waste Cooking Oil and Soap stock

Waste cooking oil refers to edible vegetable oil that is discarded after cooking food in it and can be used effectively and efficiently for the production of biodiesel. Due to its lower cost and availability, it can be collected from large agricultural units or directly from farmers. A biodiesel production rate of 8000 tons/year can be achieved in the process of transesterification of waste cooking oil. The triglyceride constituents of oil react with alcohol in presence of NaOH or other catalysts to give ester and glycerol [5]. It includes some chemical reactions which lead to enhance the effectiveness of fatty acids such as hydrolysis, oxidation and polymerization during the process of food frying (Improving the Economics of biodiesel production through the use of low Value Lipids as Feedstocks: Vegetable Oil Soapstock 2005). Soap stock is the by-product of refined vegetable oils. Due to the high content of free fatty acids in soap stock, it cannot be efficiently transformed to biodiesel and hence processed out in two steps, i.e. esterification followed by transesterification. Fatty ester acid production from any soap stock prepared in an alkali refining procedure of coconut, rapeseed, sunflower and soybean, contains about 2.5% water, soaps with strong acids undergo esterification via a lipase enzyme. Simple chemical methods have been used to yield biodiesel from a low-quality underutilized feedstock. Therefore, the product is similar in composition, engine performance and emissions are expected to be economical [6] (Fig. 1).

Fig. 1
figure 1

Flowchart of diesel and biodiesel (Production of Biodiesel from Castor Oil with Its Performance and Emission Test 2015)

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3 Characterization of Biodiesel on the Basis of Physical and Chemical Properties

It is necessary to characterize biodiesel based on some physical and chemical characteristics which need to match the standard for biodiesel by different standards of the testing method. Following are some properties discussed for various biodiesel and their blends which were found to be suitable with the standards to be used as a substitute fuel for conventional diesel.

3.1 Viscosity

The viscosity of fuel plays a crucial part in the combustion of fuel. Proper combustion and thermal efficiency of the engines are decided by the direct injection in the open combustion chamber through the nozzle and the pattern of fuel spray. Low viscosity fuel can lead to unnecessary pump leakage internally as system pressure reaches an undesirable level and affects injection of fuel during the spray atomization. Viscosity effects are more pronounced at lower engine speed and light load conditions [7]. The viscosity of biodiesel is generally higher than that of conventional diesel fuel often by a factor of two, fuel viscosity increases as the percentage of biodiesel increases in the blend. Viscosity acts as a function of temperature, many problems arise from higher viscosity range at low atmospheric temperature leading to cold starting problem of diesel engine. The increase in viscosity is mainly due to the increase in the length of the fatty acids in fatty ester or an aliphatic hydrocarbon. It has been proved in multiple researches that viscosity plays a significant role in fuel characterization. The viscosity of sorghum oil reduces sustainably after transesterification and is close to adaptable measures of petrodiesel [8]. The derivative of biodiesel blend from jatropha oil is suitable for diesel engines provided that its flash point, cloud point, kinematic viscosity and cetane number comply with international standards. Pure jatropha biodiesel, with a higher value of kinematic viscosity, cannot be utilized in diesel engines directly. Jatropha can be used after blending it with diesel fuel in a ratio up to (20–50)% [9]. Previously done research gives clear evidence that the blends comprising up to 30% (volume/volume) jatropha oil retain viscosity nearly close to diesel fuel. Furthermore, the blend comprising edible and non-edible vegetable oil has a marginally higher viscosity than that of diesel. Heating the blends reduces the viscosity range. It has been found that as the temperature increases, the value of viscosity for biodiesel and its blends decreases and becomes more suitable to be used with standard parameter. (Preparation of Biodiesel from Higher FFA Containing Castor Oil 2013) in their research on blend B70 containing 70% of biodiesel and 30% of petrol-diesel by volume, concluded that the viscosity of B70 was found to be similar to biodiesel standard. Finally, this product can be successfully used as a substitute of diesel in a diesel engine.

3.2 Flash Point, Cloud and Pour Points

Flash point is defined as the lowest temperature of a fuel at which its vapours make an ignitable mixture with air. It is an important property to be taken into consideration while producing biodiesel. Pure biodiesel results in high flash point but when blended with petrodiesel these values were brought to adaptable levels. The flash point is considered as a crucial factor for safety purposes which involve handling and storage of the fuel. It is normally specified to meet with fire regulation standards. Pure biodiesel shows a higher value of flash point and does not fit within the recommended limits, but this value can be brought down easily with increase in residual alcohol, as these two aspects are dependent over each other. The flash point used as a regulation for categorizing storage of fuels and their transport varies vividly from one region to another, so the alignment of diverse standards would possibly need a corresponding alignment to the regulations. The blends of jatropha ethyl ester were found to have lower flash point in comparison with pure biodiesel, and the property was more enhanced with the blending ratios increased [10]. B5 blend of castor oil biodiesel was found to be the best mixing ratio in terms of thermophysical properties. The flash point was also in a considerable range including other properties; however, other mixing ratios (B10, B15, B20 and B30) are slightly different than B5. It can be said that blending 5% of castor biodiesel with petrodiesel would give a great substitute of diesel fuel for CI engines. The cloud point and the pour point may be defined as the measures indicating the liquidity or fluidity of any fluid to be transferred. Therefore, they hold great significance to engines operating in cold climate. The measurement of these points specify how long a fuel can resist its ability to form small crystals (cloud) and fully solidify (pour) when allowed to rest in low temperature conditions. It is observed that the low value of these point results in better engine performances and durability. The values of pour and cloud points of neem oil biodiesel were not found within the standards required for biodiesel, but with blending, the values were quite acceptable [8].

3.3 Specific Gravity

Specific gravity is another crucial parameter for fuel. In chemical industries, relative density data is needed to design reactors for the splitting of fatty acids, for distillation units, for separation of fatty acids, conversion of fatty acids to their derivatives, and for different pipe processing units [11]. Biodiesel density is a temperature function and needs to be modelled to better understand the combustion phenomenon and other uses. The injection systems of an engine consisting of the pump and the injectors are set to orderly deliver a preset volume of diesel in the combustion chamber, and the evaluating characteristic is the fuel–air ratio [12]. The density of pure biodiesel directly depends on temperature, molar mass, free fatty acid content and water content. Jatropha oil biodiesel possesses similar characteristics to that of diesel and is increasingly being used as a fuel. Neem oil’s relative density is higher than diesel—Neem methyl ester with 6.8 viscosity has a relative density 2.6% times higher than diesel. The relative density of neem methyl ester-ethanol blends decreases with increase in the level of ethanol in the blend.

3.4 Calorific Value, Ash Content and Cetane Number

The amount of heat produced by the complete combustion of a unit mass of fuel is known as its calorific value, and it plays an important role while studying about biodiesel because it requires a large amount of heat energy is to run a diesel engine and the fuel must be capable enough to produce it. The calorific values of various biodiesel are compared in the below table. Table 5 shows that the values have a minimal difference among them, and hence almost all the categories of biodiesel listed can be used for some purpose as long as they fit the parameter requirements of the said purpose. Ash in general is described as the inorganic matter in fuel. Or, it can be said to be the residue left after the fuel undergoes complete combustion. For an appropriate fuel, the ash content of diesel and biodiesel is supposed to be about 0.02% and 0.03%, respectively. The ash content of jatropha oil was found to be 0.0999%. The ash content of JEE20, JEE100, JME20 and JME100 was found as 0.0083%, 0.0098%, 0.0081% and 0.0088%, respectively. The above results indicate that the ester diesel blends had the ash content within the recommended level [2]. It is the measure of the ignition quality of diesel fuel; higher cetane number gives shorter delay interval and greater combustibility and lower number will result in difficult starting, noise and excessive exhaust smoke. Cetane number for castor oil is 40, and after esterification, it is found to be 42 [13]. Further, this value for different biodiesel on treatment was noticed to be a little higher and in a considerable zone.

4 Conclusion

Based on above data and study, it can be concluded that biodiesel from various feedstock can surely be used as an alternative fuel with or without little modification in near future as it possesses similar characteristics that of petrodiesel. Different results from various researchers on the manufacturing of biodiesel, their availability and their properties give us a clean clue to use it as an alternative fuel. Moreover, the pure biodiesel cannot be used directly because of higher cost and other parameters related to its properties, but blending them with petrodiesel results in exact fulfilment of our need. Out of different blending ratios, the blending ratios with less percentage of biodiesel including (B5, B10, B15 and B20) conform to the standards and fulfil the measures required for substitution of petrodiesel. Out of all the diverse types of biodiesel from various feedstocks, castor oil and jatropha oil have attracted most research due to various parameters. Since jatropha can hardly be used for any other purposes than making seed oil, hence, it is commercially unviable and unfriendly for farmers. Whereas castor oil has no such drawbacks except the cost parameter but due to its application in other fields, including pharmaceutical industries, soap production, wax and grease for lubrication, hydraulic and brake fluid, etc., the cost can be compensated. Beside this accessible condition of cultivation, high oil content and other factors support its use as a substitute for diesel. Not much research work is performed with blends of castor biodiesel and conventional diesel. So there is a great opportunity for researchers to use castor oil as a substitute for diesel as a fuel.