Elsevier

Fuel

Volume 174, 15 June 2016, Pages 89-96
Fuel

Effect of antioxidant additives on the performance and emission characteristics of a DICI engine using neat lemongrass oil–diesel blend

https://doi.org/10.1016/j.fuel.2016.01.076Get rights and content

Highlights

  • Use of antioxidants is an effective technique for improving oxidation stability.

  • Two antioxidants such as BHA and BHT were used in the study.

  • BHA exhibits better oxidation stability and reduction of NOx emission than BHT.

  • CO, HC and Smoke emissions increase with the addition of antioxidants BHA and BHT.

Abstract

In this experimental investigation, the effect of antioxidant additives on the performance and the exhaust emissions of a computerized single cylinder direct injection compression ignition (DICI) engine has been studied. The test fuel used in this study was neat lemongrass oil (LGO)–diesel blend. Neat lemongrass oil is a new alternate fuel used in a diesel engine. Antioxidant additives butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) were individually dissolved at concentrations of 500, 1000, 2000 ppm by weight in LGO25 blend (75% diesel + 25% neat lemongrass oil by % volume). The emission results showed a significant reduction of NOx at the expense of increasing CO, Smoke and HC emissions. The addition of BHA at 2000 ppm with LGO25 exhibited a maximum reduction of NOx by 11% than LGO25 without any antioxidant additives. The results showed that LGO25 with antioxidant additives produced an increase in Brake thermal efficiency (BTE) and decrease in exhaust gas temperature (EGT) and specific fuel consumption (BSFC). BHA antioxidant additive exhibits a better stability than BHT in LGO25 fuel. Thus, LGO25 with added antioxidants can be used in diesel engines without any modification.

Introduction

Biofuel, an alternative to conventional petroleum based fuels, can be produced from various sources like vegetable oil, animal fats, waste oil, etc. Moreover, it has a lot of advantages such as non-toxic, biodegradable and sulfur-free. Furthermore, in various countries, significant attention has been paid in the improvement of alternate energy sources. The share of bio-fuels in the automotive industry is estimated to increase rapidly in the near future. Many developed countries have set a target of implementation of usage of B20 as fuel (Diesel 80% and 20% Biofuel) in the vehicles within the year 2020. Diesel fuel is primarily used for transportation, agriculture and electric power generation. India is a developing country; the requirement for diesel fuel is roughly six times that of gasoline, hence search for alternate to diesel is a natural option [1]. On the other hand, India is the world’s third largest energy consumer and a consumer of crude and petroleum products after the United States and China [2]. India imported 3.86 million barrels per day of crude oil last year. It is estimated that India’s import bill to fall by 21.7% to $88 billion in 2016 and 80% import dependent to meet its oil needs only [3].

India has great potential for production of bio-fuels from non-edible oil seeds like, Jatropha curcas, Pongamia pinnata, Rubber seed, Cotton seed, Neem, etc. If the bio-fuels share the energy needs by 20%, $17.6 billion could be saved in the import bill, thereby, improving the country’s economy. Furthermore, in rural and remote areas, non-availability of grid power, edible/non-edible oil source is one of the power generations for irrigation and electrification. In these remote areas, availability of various types of oils grown/produced locally, but it may not be possible to chemically process them due to practical difficulties in rural areas. Hence, direct blending with diesel fuel substitutes is a promising solution [4]. While most of the properties of neat lemongrass oil are comparable to pure diesel fuel and can be used directly in diesel engines without any engine modifications [5], [6].

The exhaust gases from compression ignition engines are composed of a large number of organic and inorganic solid, liquid and gaseous chemical species. All over the world, these exhaust gases from automobiles lead to the global warming problems. It causes deterioration of lung function, cardiovascular diseases, neurodegenerative disorders and even heart attacks [7]. A great challenge for the automotive industry is the emission of NOx and particulate matter. Diesel vehicles are a significant source of NOx and PM emissions [8]. A notable technique for the reduction of NOx emission in the diesel engine is mixing of antioxidant additives with biodiesel fuels. It is primarily used to increase the stability of biodiesel for long term storage. Biodiesel is affected mainly by the autoxidation in the presence of atmospheric oxygen, which leads to the formation of hydroperoxides (ROOH) [9]. Once the hydroperoxides have formed, the biofuel gets decomposed and then inter-react to form numerous secondary oxidation products. These products consist of higher molecular-weight oligomers, often termed as polymers. Antioxidants can be classified into various groups: free radical terminators, metal-ion chelators capable of catalyzing lipid oxidation, or oxygen scavengers that react with oxygen in closed systems. Free-radical terminators are considered as primary antioxidants; they react with high-energy lipid radicals and convert them into thermodynamically more stable products [10], [12]. Both phenolic and amine antioxidants are the most used antioxidants. They are considered as free radical terminators. The effectiveness of the antioxidants is expressed by the term ‘stabilization factor’. It is given by F = IPx/IP0, where IPx is the induction period in the presence of the antioxidant and IP0 is the induction period in its absence [11]. The free radical terminators consist of highly labile hydrogen, which is rapidly contributed to a peroxyl radical (ROO) which interferes with the lipid-oxidation process [12].

Borris et al. [13] have used oxygenated additives of EtilTerbutilEter (ETBE) and Diglyme in proportions of 5%, 10% and 15% in diesel fuel in the TDI diesel engine. The test results showed a significant increase in BTE and SFC. It was reported that an increase in or constant NOx emissions depending on the amount of additives in the mixture, engine speed and load condition. Ileri and Kocar [14] have conducted tests on turbocharged direct injection diesel engine with antioxidant additives butylated hydroxynaisole (BHA), butylated hydroxytoluene (BHT), ter-butylhydroquinone (TBHQ), and 2-ethylhexyl nitrate (EHN) in biodiesel derived from canola oil. The test results indicated that antioxidant additives have a potential for increasing oxidation stability and decreasing NOx emissions. It was concluded that TBHQ is a more effective antioxidant for oxidation stability and EHN is a promising additive for decreasing NOx emissions at the expense of increasing CO and HC emissions. Yang et al. [15] have investigated using biodiesel from pine oil with the ignition promoters of IAN (iso-amyl nitrate) and DTBP (di-tertiary butyl peroxide). The test results showed a reduction of NOx emission by 12.8% and 19.2% with IAN and DTBP promoters respectively. Further, it was observed that DTBP is more effective in reducing NOx emission with a significant reduction in CO and HC emissions by 40% and 34% respectively. Rizwanul Fattah et al. [12] have conducted tests using biodiesel from palm oil with two monophenolic antioxidants of 2,6-di-tert-butyl-4methylphenol (BHA) and 2(3)-tert-butyl 4-methoxy phenol (BHT) at 1000 ppm concentration. The addition of BHA and BHT resulted in a mean reduction in BSFC of 0.64% and 0.18% respectively. A considerable reduction in NOx emission of 12.6% and 9.8% with BHA and BHT respectively was also seen. More experimental investigations [16], [17], [18], [19], [20], [21], [22] also proved that a significant reduction in NOx emissions was achieved with the addition of antioxidants. The literature study, overall observes that antioxidant additives influence a considerable reduction of NOx emission, but with an increase in smoke, CO and HC emissions. The biofuel oxidation stability also improved with the use of antioxidant additives.

The prospect of using new alternative biofuel in diesel engine has influenced to study the practicality of using lower cetane biofuel, neat lemongrass oil, in a diesel engine. With reference to the literatures studied, a considerable research work has not been reported to explore neat lemongrass oil as an alternate fuel and hence all the properties were studied to ensure its suitability of operation in a diesel engine. Lemongrass oil has a comparable calorific value (83%) with diesel and therefore, it can be blended with diesel in higher proportions. Apparently, from with neat lemongrass oil-diesel blends in a diesel engine, it was observed that higher proportions of lemongrass oil with diesel fuel exhibited higher NOx emissions and the more engine vibrations. However, lower cetane number of lemongrass oil affected the fuel ignition. Therefore, in this study, it was optimized the use of optimum blend, LGO25 (25% neat lemongrass oil + 75% diesel on volumetric %) in a diesel engine. The two antioxidant additives of BHA (2,6-di-tert-butyl-4-methylphenol) and BHT (2(3)-tert-butyl-4-methoxy phenol) were used with the LGO25 in the different concentrations of 500, 1000 and 2000 ppm. Both BHA and BHT are phenolic-type antioxidants. The current study focuses on the engine performance and emission characteristics of the direct injection single cylinder diesel engine. The impact of the antioxidant additives was investigated and compared with LGO25 as well as standard diesel. Further, it was observed that engine does not require any major modifications or changes in the fuel handling and delivery systems.

Section snippets

Test fuel: Lemongrass oil

The diesel fuel was used as base fuel. LGO25 was taken as test fuel. The neat lemongrass oil used in this study was purchased from a local manufacturer. It contains 70–80% Citral. Its chemical formula is C10H16O and occurs in essential oils of plants. In India, lemongrass (cymbopogon flexuosus), also called as cochin grass or Malabar grass is an aromatic and a fast growing grass family (Poecia) with more than 140 species all over the world. The main elements are citral, limonene, terpineol,

Oxidation stability

Table 7 shows details of the effect of antioxidant additives on the oxidation stability of LGO25 with respect to antioxidant concentration. The Biodiesel-Rancimat method (accelerated oxidation test) was used to determine the oxidation stability of LGO25 with and without antioxidant additives. Oxidation stability of LGO25 with antioxidants increased more than LGO25 without antioxidant additives. BHA was found more effective than BHT at a concentration of 2000 ppm. BHT was found to be the least

Conclusion

The main objective of the study was to investigate the effect of antioxidant additives on diesel engine performance and emission characteristics using neat lemongrass oil–diesel blend. Based on the results, the following conclusions can be drawn.

  • The addition of antioxidant additives increased the kinematic viscosity, density, and flash point but reduced the calorific value.

  • BHA produced better stabilization compared to BHT in LGO25.

  • Brake thermal efficiency increases by 1.29% at LGO25+BHA and

Acknowledgement

The authors would like to thank the Management of Panimalar Engineering College Chennai and Anna University, Chennai for their continuous support to carry out this research work.

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