Elsevier

Energy

Volume 36, Issue 12, December 2011, Pages 6862-6866
Energy

A modified diesel engine for natural gas operation: Performance and emission tests

https://doi.org/10.1016/j.energy.2011.10.009Get rights and content

Abstract

A diesel engine was modified for natural gas operation to optimize performance using gaseous fuel. A variation of combustion ratios (CR) including 9.0:1, 9.5:1, 10.0:1 and 10.5:1 was utilized to evaluate engine performance and emissions from the same engine over the engine speeds between 1000 and 4000 rpm. Tested engine performance parameters include brake torque, brake power, specific fuel consumption (SFC) and brake thermal efficiency. Emissions tests recorded total hydrocarbon (THC), nitrogen oxides (NOx) and carbon monoxide (CO). The results showed that a CR of 9.5:1 had the highest thermal efficiency and the lowest SFC while a CR of 10:1 showed a high torque at low speed. THC emissions were directly proportional to the CR. NOx emissions increased with increasing CR and then declined after a CR of 10:1.

Highlights

► A diesel engine for natural gas operation to optimize performance using gaseous fuel. ► A variation of combustion ratios (CR) was utilized to evaluate engine performance and emissions. ► CR of 9.5:1 had the highest thermal efficiency and the lowest SFC. ► CR of 10:1 showed a high torque at low speed. ► THC and NOx emissions were directly proportional to the CR.

Introduction

Over past decades, increased energy demand has resulted in higher fossil fuel consumption and, consequently, higher emissions. Presently, it is estimated that combustion of fossil fuels releases greenhouse gases, especially CO2, at a rate of about 7 billion tons each year [1]. Modifications have been developed and mandated to reduce emissions; examples include the improvement of energy-conversion efficiency, technology innovations, uses of renewable energies, etc.

In many countries, including Thailand, diesel consumption is much higher than that of other fuels due to its use as the main fuel for mass transportation. Due to its combustion characteristics, the diesel engine shows higher thermal efficiency than the gasoline engine. However, the exhaust emissions from the diesel engine are higher. Several studies have been published showing the reduction of diesel consumption and emissions; blending diesel with biodiesel [2], [3], [4], [5], ethanol [6], ethers [7], and dual injection with natural gas [8], [9], [10], [11]. The results from these studies show less emissions at constant power output.

Natural gas offers several advantages such as clean combustion, high octane number (approximately 120), high availability, and attractive price. Additionally, its relatively high auto-ignition temperature is suitable for higher compression engines [9], [10]. For these reasons, natural gas is expected to find wide spread use in locomotive engines. Previous studies investigated the characteristics of dual fuel operation in unmodified or minor-modified gasoline engines [12], [13] and diesel engines [8], [9]. Dual injection of natural gas in gasoline engine leads to lower unburned hydrocarbon and carbon monoxide (CO) emissions, at the cost of reduced horse power and thermal efficiency. The combustion characteristics of diesel engine with natural gas/diesel fuels showed positive effect on thermal efficiency, total brake-specific fuel consumption, soot and NO emissions [8], [9]. However, the reports indicated that such dual operation system could not reach high speed operation as it could be gained while using only diesel engine. Therefore, the modification of the engine may offer an alternative way to trade off these effects.

The main objective of the present work is the modification of a diesel engine for natural gas operation to maximize output using gaseous fuel. The variation of combustion ratios was conducted to evaluate engine performance and emissions from the same engine. Engine performance includes brake torque, brake power, specific fuel consumption (SFC), and brake thermal efficiency. Emissions testing included total hydrocarbon (THC), nitrogen oxides (NOx), and carbon monoxide (CO) measurements.

Section snippets

Experimental

As previously stated, the primary purpose of this experimental investigation was to compare engine performance and emissions between a standard diesel engine and a modified one which used natural gas as the main fuel. The basic properties of the fuels used are given in Table 1, Table 2. The engine used in the present study was Daedong indirect injection diesel engine. The detailed specifications of this engine are shown in Table 3. The engine was loaded by a 130-kW Hwanwoong eddy current

Comparison of the diesel and natural gas engines

Engine outputs including engine brake power, brake torque, SFC and thermal efficiency of the diesel and natural gas engines are showed in Fig. 2, Fig. 3, Fig. 4, Fig. 5. Fig. 2 shows the influence of engine speed on the brake torque for both engines. As the engine speed increases, the brake torque continuously decreases as a result of a decrease in volumetric efficiency [14]. Compared to a diesel engine at the same engine speed, the natural gas engine shows higher brake torque. The difference

Conclusion

The modification of a diesel engine for natural gas operation was studied. A range of combustion ratios was used to evaluate engine performance and emissions using a natural gas fuel. The following are this study’s conclusions:

  • 1.

    Using the same engine, natural gas showed improved performance over the diesel engine, approximately 5.67%–13.07%.

  • 2.

    For CRs ranging from 9:1 to 10.5:1, a CR of 9.5:1 had the highest thermal efficiency at speeds between 1500 and 2500 rpm.

  • 3.

    CR of 10:1 showed a high torque at

Acknowledgment

The authors gratefully acknowledge the contribution of the College of Industrial Technology, King Mongkut’s University of Technology North Bangkok for the financial support.

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