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Publication Title | Performance Analysis of the Organic Rankine Cycle (ORC) System under Engine Various Operating Conditions

Organic Rankine Cycle

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DOI: 10.7763/JOCET.2015.V3.220

340

Journal of Clean Energy Technologies, Vol. 3, No. 5, September 2015

Performance Analysis of the Organic Rankine Cycle (ORC) System under Engine Various Operating Conditions

Kai Yang and Hongguang Zhang



Abstract—Though experiments, variation of a diesel engine exhaust energy is studied, a set of ORC system is designed and set up. The variation of running performance of an ORC (organic Rankine cycle) system under engine varying working conditions is analyzed, the effects of evaporating pressure on the ORC system is discussed, the improvement extent of engine thermal efficiency, brake specific fuel consumption (BSFC) after the engine is coupled with a set of an ORC system is studied. The research shows that, when evaporating pressure being 3MPa, engine speed being 2200r/min and engine torque being 1200N·m separately, the net power output of the ORC system, engine thermal efficiency increasing ratio (ETEIR), and the Improvement ratio of BSFC all hits the maximum values, being 22.41kW, 8.085%, 7.423% respectively.

Index Terms—Vehicle diesel engine, waste heat recovery, organic Rangine cycle, various operating conditions.

I. INTRODUCTION

IC (internal combustion) engines have taken away a good deal of oil resources, while their thermal efficiencies still have deep potential to improve. Most energy released from the fuel combustion in the cylinder has been carried off by the exhaust and cooling medium, wasting energy and causing severe environmental problems [1]. Therefore, how to highly effectively recover and utilize this kind of energy is very necessary, with which the energy consumption and pollutant emission all can be reduced.

The ORC technology, used for heat-work conversion, can convert the medium-low waste heat into useful work for output, and has been studied and applied in many areas [2]-[6]. Pierobon et al. [7] designed an organic Rankine cycle system to recover the waste heat from a gas turbine. El-Emam et al. [8] analyzed the running performances on a geothermal regenerative ORC system. Wang et al. [9] designed an organic Rankine cycle system driven by solar energy. Marion et al. [10] analyzed the effects of wind, ambient temperature and solar radiation on the simultaneous productions of mechanical work and heat by a solar Rankine cycle.

Currently, some scholars are considering how to use the ORC technology to recover the exhaust heat of the IC engine [11]-[14]. Peris et al. [15] utilized an organic Rankine cycle system to recover the coolant energy of engines. Meinel et al. [16] recovered exhaust energy from

Manuscript received June 30, 2014; revised August 26, 2014.

The authors are with the Beijing University of Technology, Pingleyuan No.100, 100124 Beijing, China (e-mail: ykai104@163.com, zhg5912@263.net).

engines by using an organic Rankine cycle system. Hajabdollahi et al. [17] studied the thermal efficiency and cost of the diesel engine–ORC system. Domingues et al. [18] analyzed the exhaust waste heat recovery potential by using a Rankine cycle. In conclusion, ORC system can effectively recover the waste heat, thereby, increase the engine thermal efficiency.

In this paper, we have achieved a full set of experiment data of a diesel engine in the whole operating range, also we studied variation of the exhaust energy and the running performance of the ORC system in engine varying range. Afterwards, we discussed the effects of the evaporating pressure on the ORC system performance, and analyzed the improve degree of the diesel engine thermal efficiency when the engine is coupled with an ORC system.

II. DIESEL ENGINE EXPERIMENTS

With experiment, we achieved the test data of a six-cylinder four-stroke vehicle diesel engine. To highly effectively recover and utilize the waste heat in the engine whole operating range, we have studied the variation of the exhaust energy in different working conditions. Through equation (1), the exhaust energy can be computed.

where, Qava



Qava  cpmexh(Texh_1-Tmin) (1)

is the maximum exhaust energy of the diesel

energy, cp is the constant-pressure specific heat of the

diesel engine, mexh is the mass flux, Texh_1 is the exhaust

temperature, Tmin is the minimum temperature the exhaust

can reach to when go through the heat exchanger. Via experiment, we achieved linear relation by matching the cp

with the exhaust temperature.

cP  0.00025Texh_1  0.99 (2)

Fig. 1 is the variation of the available exhaust energy under engine varying working conditions. With the increase of the engine torque and speed, the available exhaust energy increase gradually. When engine speed being 2200r/min and engine torque being 1200N·m, the available exhaust energy hits the maximum value, which is roughly 290kW. The rated output power of this diesel engine is 280kW.

Fig. 2 is the variation of the Brake Specific Fuel Consumption (BSFC) of the diesel engine. As can be seen,

Image | Performance Analysis of the Organic Rankine Cycle (ORC) System under Engine Various Operating Conditions



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