Preparation, characterization, engine combustion and emission characteristics of rapeseed oil based hybrid fuels

doi:10.1016/j.renene.2013.05.008

Renewable Energy

Volume 60, December 2013, Pages 98-106

https://doi.org/10.1016/j.renene.2013.05.008 Get rights and content

Highlights

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A hybrid fuels consisting of rapeseed oil/diesel blend, 1% aqueous ethanol and a surfactant (oleic acid/1-butanol mixture) was prepared.
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The phase boundaries of hybrid fuels were determined by titration.
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The main properties of the hybrid fuels were measured.
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The combustion characteristics of the engine were calculated and analyzed.
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The performance and emissions characteristics of the engine were compared and studied.

Abstract

In this study, hybrid fuels consisting of rapeseed oil/diesel blend, 1% aqueous ethanol and a surfactant (oleic acid/1-butanol mixture) were prepared and tested as a fuel in a direct injection (DI) diesel engine. The main fuel properties such as the density, viscosity and lower heating value (LHV) of these fuels were measured, and the engine performance, combustion and exhaust emissions were investigated and compared with that of diesel fuel. The experimental results showed that the viscosity and density of the hybrid fuels were decreased and close to that of diesel fuel with the increase of ethanol volume fraction up to 30%. The start of combustion was later than that of diesel fuel and the peak cylinder pressure, peak pressure rise rate and peak heat release rate were higher than those of diesel fuel. The brake specific fuel consumption (BSFC) of hybrid fuels was increased with the volume fraction of ethanol and higher than that of diesel. The brake specific energy consumption (BSEC) was almost identical for all test fuels. The smoke emissions were lower than those for diesel fuel at high engine loads, the NO_x emissions were almost similar to those of diesel fuel, but CO and HC emissions were higher, especially at low engine loads.

Introduction

The depletion of petroleum energy resources as well as their inherent environmental concerns has led to the pursuit of renewable biofuels. Vegetable oils are being considered as such an alternative fuel because of their renewable and non-toxic nature. Researchers have evaluated the use of sunflower, safflower, soybean, cottonseed, rapeseed and orange oils as potential renewable fuel sources [1], [2], [3], [4], [5], [6].

The injection, atomization and combustion characteristics of vegetable oils in diesel engines are significantly different from those of diesel fuel. The direct use of vegetable oils is generally considered to be unsatisfactory and impractical for diesel engines. The high viscosity of vegetable oil interferes with the injection process and leads to poor fuel atomization. The inefficient mixing of fuel with air contributes to incomplete combustion. The high flash point, oxidative and thermal polymerization lead to more deposit formation, carbonization of injector tips, ring sticking, lubrication oil dilution and degradation. The combination of high viscosity and low volatility of vegetable oils causes poor cold engine start up, misfire and ignition delay period. It is therefore unsuitable to use straight vegetable oils in diesel engines [7], [8], [9], [10].

To overcome these problems caused by the high viscosity of vegetable oils, a number of techniques have been used. These include vegetable oil/diesel blends, increasing the vegetable oil temperature, pyrolysis, vegetable oil transesterification to fatty alkyl esters or biodiesel, and vegetable oil-based micro-emulsions to make the hybrid fuel [11], [12], [13], [14], [15], [16]. Attaphong et al. [17] produced a kind of vegetable oil based micro-emulsions as an alternative method of reducing viscosity and evaluated the phase behavior of carboxylate-based extended surfactant micro-emulsion systems with the goal of formulating optimized systems for biofuel. The results indicated that carboxylate-based extended surfactants were able to form micro-emulsions, thereby eliminating the phase separation and precipitation. In addition, fuel properties such as viscosity and temperature dependence were favorable and thus supported the development of these surfactant-based fuel systems for use in diesel engines. Frank et al. [18] evaluated the effects of croton oil-butanol-diesel blends on the performance and emissions of diesel engine. It was observed that BSEC of blends was found to be higher when compared with that of diesel fuel. Butanol containing blends showed higher peak cylinder pressure and heat release rate comparable to that of diesel fuel on higher engine loads. Carbon dioxide (CO₂) and smoke emissions of the blends were lower in comparison to diesel fuel. Qi et al. [19] used oleic acid as emulsifier to produce biodiesel/diesel-methanol micro-emulsions and evaluated the performance and combustion characteristics. The results indicated that the power and torque outputs of micro-emulsions were slightly lower than those of diesel fuel. The smoke and CO emissions were evidently decreased, and NO_x and HC emissions were almost similar to those of diesel fuel. Lei et al. [20] produced a novel mixed emulsifier based on biofuel and castor oil, and studied the effects of the ethanol-diesel blends with the emulsifier on the performance and emission characteristics of a diesel engine. The results indicated that the ethanol-diesel blend can keep its physical stability at a wide range of temperatures with the emulsifier. The smoke emission was reduced significantly and the NO_x emission decreased slightly, while the HC emission increased. Singh et al. [21] produced one kind of hybrid fuel consisting of coconut oil, aqueous ethanol and a surfactant, and investigated the fuel properties, engine performance and exhaust emissions. The experimental results showed that the effective thermal efficiency of the hybrid fuels was comparable to that of diesel. The exhaust emissions were lower than those for diesel, except CO emissions. Kumar et al. [22] studied the micro-emulsion of linseed oil and mahua oil with neat diesel fuel and alcohol in varying proportion, evaluated their properties, performance and emission characteristics in a diesel engine, and concluded that the micro-emulsion of vegetable oil can partially substitute the diesel fuel with no difficulty.

Some literature revealed that vegetable oil had the environmentally advantageous and more energy efficient than corresponding biodiesel. Esteban et al. [23] concluded that Spanish rapeseed oil showed the environmental benefits instead of biodiesel by using life-cycle assessment. The energy return on investment index indicated a more energy efficient for rapeseed oil as compared to biodiesel due to the production of biodiesel which required more complex processes. Therefore, rapeseed oil was a useful option as a produced biofuel that additionally closed the cycles of all generated co-products. Hossain et al. [24] indicated that raw plant oils had considerable advantages over corresponding biodiesel as regards life-cycle energy and greenhouse gas emission analyses. Depending on either primary energy or fossil energy requirements, the life-cycle energy ratio of raw plant oil was in the range of 2–6 times higher than that of biodiesel. Moreover, raw plant oil had the highest potential of reducing life-cycle greenhouse gas emissions as compared to biodiesel. In addition, biodiesel was formed by the transesterification reaction of triglycerides with alcohols in the presence of a catalyst and produced glycerol as a co-product. Since glycerol was expensive to purify or convert to a value-added product, it caused problems of disposal and environmental concern [25].

The objectives of this study were to prepare rapeseed oil/diesel-ethanol hybrid fuels using the micro-emulsification technique, and to evaluate their relevant properties, engine combustion and exhaust emission characteristics. After describing the methodology for the preparation of the hybrid fuels, the main chemical and physical properties of the fuels were analyzed. The results of the engine combustion and the emission characteristics of a DI diesel engine operated on these hybrid fuels were then reported and analyzed.

Section snippets

Hybrid fuels preparation

In this study, the diesel fuel, rapeseed oil (RSO), ethanol, and oleic acid used in this study was obtained commercially from a local company and used in the experiments as the blending stock. The diesel fuel used in this experiment was 0# diesel in China. To solve the problem of the high viscosity of vegetable oils, micro-emulsions with solvents such as methanol, ethanol and 1-butanol have been investigated. A micro-emulsion is defined as a colloidal equilibrium dispersion of optically

Ternary phase diagram and fuel properties

The miscibility curve was plotted as the boundary between two phase and single phase micro-emulsions, as illustrated in Fig. 2. At temperatures of 15 °C, the formulations above the miscibility curve existed as one visible phase in the form of thermodynamically stable micro-emulsions, while those below the curves would be unstable and had two visible immiscible phases. The order of adding the fuel constituents to one another was not particularly critical. Though the micro-emulsion formed

Conclusions

In this study, the preparation, characterization, engine performance, combustion and emission characteristics of a rapeseed oil/diesel based hybrid fuel were investigated. The following conclusions can be drawn:

(1)
Oleic acid/1-butanol mixture can be used as an effective surfactant to prepare a stable and homogenous micro-emulsion of rapeseed oil/diesel blend and aqueous ethanol of 99% purity. The viscosity and density of hybrid fuels can be reduced to close to that of diesel fuel using the

Acknowledgments

The authors wish to express their deep thanks to the scientific research foundation for the returned overseas of China and the colleagues in the Engine Lab. of Korea Advanced Institute of Science and Technology.

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Preparation, characterization, engine combustion and emission characteristics of rapeseed oil based hybrid fuels

Highlights

Abstract

Introduction

Section snippets

Hybrid fuels preparation

Ternary phase diagram and fuel properties

Conclusions

Acknowledgments

Renew Sustain Energy Rev

Renew Energy

Energy Convers Manage

Renew Energy

Energy Policy

Renew Energy

Energy

Renew Sustain Energy Rev

Appl Therm Eng

Biomass Bioenergy

Appl Therm Eng

Appl Energy

Renewable Energy

Fuel

Fuel

Appl Energy

Fuel

Renewable Energy

Biomass Bioenergy

Renew Energy

Bioresour Technol

Fuel

Fuel