Elsevier

Renewable Energy

Volume 33, Issue 5, May 2008, Pages 871-882
Renewable Energy

Performance, emission and economic assessment of clove stem oil–diesel blended fuels as alternative fuels for diesel engines

https://doi.org/10.1016/j.renene.2007.06.009Get rights and content

Abstract

In this study the performance, emission and economic evaluation of using the clove stem oil (CSO)–diesel blended fuels as alternative fuels for diesel engine have been carried out. Experiments were performed to evaluate the impact of the CSO–diesel blended fuels on the engine performance and emissions. The societal life cycle cost (LCC) was chosen as an important indicator for comparing alternative fuel operating modes. The LCC using the pure diesel fuel, 25% CSO and 50% CSO–diesel blended fuels in diesel engine are analysed. These costs include the vehicle first cost, fuel cost and exhaust emissions cost. A complete macroeconomic assessment of the effect of introducing the CSO–diesel blended fuels to the diesel engine is not included in the study. Engine tests show that performance parameters of the CSO–diesel blended fuels do not differ greatly from those of the pure diesel fuel. Slight power losses, combined with an increase in fuel consumption, were experienced with the CSO–diesel blended fuels. This is due to the low heating value of the CSO–diesel blended fuels. Emissions of CO and HC are low for the CSO–diesel blended fuels. NOx emissions were increased remarkably when the engine was fuelled with the 50% CSO–diesel blended fuel operation mode. A remarkable reduction in the exhaust smoke emissions can be achieved when operating on the CSO–diesel blended fuels. Based on the LCC analysis, the CSO–diesel blended fuels would not be competitive with the pure diesel fuel, even though the environmental impact of emission is valued monetarily. This is due to the high price of the CSO.

Introduction

Most of the energy used in the world is supplied by fossil fuels. Burning of fossil fuels generates waste materials, mainly emissions to the atmosphere in the form of exhaust gases and dust, as well as some ash. These emissions have hazardous effects on the environment, some of them locally, others with more widespread or even global impact. Not only does the continued use of fossil fuels pose a serious threat to the environment, but also liquid hydrocarbon fuel deposits are exhausted. These problems of fuel diminishing and negative environmental impact of fuel can be addressed by using of renewable biofuels.

A large amount of energy consumed in Tanzania is imported. Tanzania is seeking to utilize its renewable energy resources, in order to alleviate the increasing import burden of energy and adapt a sustainable approach towards energy application.

Clove tree, which is a kind of biomass, is one of the most commonly cultivated plants in Tanzania. Clove products are very important sources not only for food and pharmaceutical products but also for biomass fuel production. All parts of the clove plant (stalk, stem, leaf, etc.) can be evaluated in energy applications.

The cloves generate substantial quantity of solid by-products known as clove stems, which are less commercial. With some additional processing clove stems can produce clove stem oil (CSO). It is used as a less expensive replacement for clove oil. The identification of the local market for the applications of CSO could add value to the clove crop which has been struggling in the world market to retain a good price. This will motivate the clove farmers and enhance the clove production, thus generating more revenue for the farmers. The utilization of the by-product of cloves towards bio-oil production for an alternative fuel for diesel engines could provide an inexpensive fuel and minimize Tanzania's dependence on imported petroleum base fuels. CSO is non-edible oil; hence it could be reasonable to investigate the potentiality of the usage of CSO as an alternative fuel for diesel engines.

In order to understand all tangible and intangible benefits and promote the application of CSO in Tanzania, a comprehensive analysis of the economic assessment of the CSO–diesel blended fuels as the alternative fuels for diesel engine from a social standpoint is required. A comparison of just the fuel cost per mile or kilometre without consideration of environmental externalities and other costs can be misleading and can result in erroneous conclusions. Therefore, the aim of this study is to fill the current gap in literature and increase the knowledge regarding the performance, emission formation and economic assessment of the CSO–diesel blended fuels as the alternative fuels for diesel engine. Our recent study [1] of the comparative performance and emissions study of a direct injection diesel engine using blends of diesel fuel with CSO is extended to incorporate the economic assessment of the CSO–diesel blended fuels as the alternative fuels for diesel engine.

Section snippets

Oil extraction process

CSO is obtained by distillation. Firstly, the clove stems are placed in a large stainless-steel vessel, separated into layers to reduce compression. Steam is then passed upwards through the vessel, boiling the clove stems and carrying away with it the raw CSO. The steam with raw CSO is condensed and much of the remaining water runs off. The raw CSO is then further purified by a process of partial distillation and the final oil is obtained after filtration. Tests are carried out on the finished

Fuel properties

There are a number of fuel properties that are essential to the proper operation of diesel engine. The addition of any CSO to diesel fuel affects certain key properties with particular reference to blend stability, viscosity and lubricity, energy content and cetane number (CN). These modifications of fuel may change the fuel spray characteristics, combustion characteristics and emissions formation. Therefore, before the engine testing was embarked, basic physical, chemical and fuel related

Experimental equipment and procedures

Testing was conducted on a four cylinder, four stroke, naturally aspirated, water cooled, direct injection Isuzu Diesel engine with a bore of 93 mm, stroke of 92 mm and compression ratio of 18.4:1. The engine was directly coupled to an eddy current dynamometer using a flexible coupling and a stub shaft assembly. The maximum torque of the engine was 162 Nm at 2000 rpm and the rated power was 43 kW at 2800 rpm. No adjustment was made at the fuel injection timing, i.e. at 20° before top dead centre

Framework for economic analysis of CSO–diesel blend fuels

For a fair comparison of the different operating modes, all costs (direct and indirect costs) that will be incurred over the lifetime of the vehicle should be taken into account. This can be achieved by using a societal life cycle cost (LCC) technique. LCC is the systematic, analytical process of comparing alternatives from original source to final end, with the objective of choosing the best alternative. The LCC key cost components are summarized in the flowchart of Fig. 1.

The LCC of vehicle

Fuel properties

The important properties of CSO are found out and compared with that of the pure diesel fuel (Table 1). It can be seen that the properties of CSO are quite comparable to that of the pure diesel fuel. The viscosity of CSO lies between the minimum and maximum required values of the pure diesel fuel. It has very low CN and high density. The energy content of CSO (33.55 MJ/kg) is slightly lower than that of the pure diesel fuel (43 MJ/kg). The energy content of CSO–diesel blended fuels decreases as

Conclusions

In this study the performance, emission and economic evaluation of using the CSO–diesel blended fuels as the alternative fuels for diesel engine has been carried out. Experiments were performed to evaluate the performance and emissions of the CSO–diesel blended fuels as the alternative fuels for diesel engine. The societal LCC was chosen as an important indicator for comparing different operating modes. The findings of the study are summarized below as follows:

  • The CN of CSO prohibits its direct

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