Experimental investigation of hydrocarbon mixtures to replace HFC-134a in an automotive air conditioning system

Abstract

This paper presents an experimental study on the application of hydrocarbon mixtures to replace HFC-134a in automotive air conditioners. The hydrocarbons investigated are propane (R290), butane (R600) and isobutane (R600a). The measured data are obtained from an automotive air conditioning test facility utilizing HFC-134a as the refrigerant. The air conditioner, with a capacity of 3.5 kW driven by a Diesel engine, is charged and tested with four different ratios of hydrocarbon mixtures. The experiments are conducted at the same surrounding conditions. The temperature and pressure of the refrigerant at every major position in the refrigerant loop, the temperature, flow rate and humidity of air, torque and engine speed are recorded and analyzed. The parameters investigated are the refrigeration capacity, the compressor power and the coefficient of performance (COP). The results show that propane/butane/isobutane: 50%/40%/10% is the most appropriate alternative refrigerant to replace HFC-134a, having the best performance of all the hydrocarbon mixtures investigated.

Introduction

Stratospheric ozone absorbs the sun’s high energy ultraviolet rays and protects both humans and other living things from exposure to ultraviolet radiation. Results from many researches show that this ozone layer is being depleted. The general consensus for the cause of this event is that free chlorine radicals remove ozone from the atmosphere, and later, chlorine atoms continue to convert more ozone to oxygen. The presence of chlorine in the stratosphere is the result of the migration of chlorine containing chemicals. The chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are a large class of chemicals that behave in this manner. These chemicals have many unusual properties, for example, non-flammability, low toxicity and good material compatibility, which have led to their common widespread use by both consumers and industries around the world, especially as refrigerants in air conditioning and refrigerating systems.

Since the discovery of the depletion of the earth’s ozone layer and as a result of the 1992 United Nations Environment Program meeting, the phase out of CFC-11 and CFC-12, used mainly in conventional refrigeration and air conditioning equipment, was expected by 1996 and that of the HCFCs is expected after 2030 [1]. Many corporations have been forced to find alternative chemicals to CFCs and HCFCs. Because the thermophysical properties of HFC-134a are very similar to those of CFC-12, and it is a non-toxic, environmentally safe refrigerant, the American Household Appliances Manufacturers have recommended HFC 134a as a potential replacement for CFC-12 in domestic refrigeration [2]. However, while the ozone depletion potential (ODP) of HFC-134a relative to CFC-11 is very low (<5 × 10⁻⁴), the global warming potential (GWP) is extremely high (GWP = 1300) (see Table 1). For this reason, the production and use of HFC-134a will be terminated in the near future.

Over the years, new refrigerant mixtures to replace the conventional refrigerants in refrigeration systems have been studied. However, the works found in literature focused on the study to replace the conventional refrigerant in domestic refrigerators. Jung and Radermacher [3] performed a computer simulation of single evaporator domestic refrigerators charged with many pure and mixed refrigerants. The study attempted to find the best potential replacement for CFC-12. James and Missenden [4] studied the use of propane in domestic refrigerators. Energy consumption, compressor lubrication, costs, availability, environmental factors and safety were criteria for investigation. The results revealed that propane showed as an attractive alternative to CFC-12. Richardson and Butterworth [5] determined the performance of a vapor compression refrigeration system working with propane and a mixture of propane and isobutane. The obtained performance was higher than that obtained from CFC-12 under the same experimental conditions.

Alsaad and Hammad [2] investigated the performance of a medium size CFC-12 domestic refrigerator working with a propane/butane mixture experimentally and determined the refrigeration capacity, compressor power and coefficient of performance (COP). The results indicated the successful application of the mixture of propane and butane for replacing CFC-12 in domestic refrigerators. Jung et al. [6] examined the performance of a mixture of propane and isobutane for use in refrigerators. A thermodynamic analysis showed that the coefficient of performance of the system increased up to 2.3% as compared to CFC-12, the tests being run at a mass fraction of propane ranging between 0.2 and 0.6. Tashtoush et al. [7] presented an experimental study on the performance of domestic vapor compression refrigerators with new hydrocarbon/hydrofluorocarbon mixtures as refrigerants for replacement of CFC-12. The results revealed that a mixture of butane, propane and HFC-134a gave an excellent performance.

Lee and Su [1] conducted an experimental study on the use of isobutane in a domestic refrigerator. The results showed that the coefficients of performance were comparable with those obtained when CFC-12 and HCFC-22 were used as refrigerants. Akash and Salid [8] studied the performance of LPG obtained from the local market (30% propane, 55% n-butane and 15% iso-butane by mass) as an alternative refrigerant to CFC-12 in domestic refrigerators. The experiments were done with LPG at various mass charges of 50, 80 and 100 g. The results showed that a mass charge of 80 g gave the best performance.

Recently, Wongwises and Chimres [9] presented an experimental study on the application of a mixture of propane, butane and isobutene to replace HFC-134a in a domestic refrigerator. The results showed that the mixture of propane/butane 60%/40% was the most appropriate alternative refrigerant.

All the aforementioned researches paid attention to the use of hydrocarbon substances in domestic refrigerators. Regarding the use of hydrocarbon substances in automotive air conditioning systems, there has been only one work up to now, which was conducted by Jung et al. [10]. They studied the use of HCFC-22, HFC-134a, HCFC-142b, RE-170 (dimethylether), HC-290 (propane) and HC-660a (isobutene) mixed in different ratios as refrigerants for the replacement of CFC-12. The test results show that the HFC-134a/RE-170 mixture was the most suitable alternative to CFC-12.

Because hydrocarbons, for example liquefied petroleum gas (LPG), are environmentally acceptable alternative substances and cheap in nature, their use as a refrigerant in automotive air conditioners is very attractive. As mentioned above, very little information in the open literature is currently available on the use of hydrocarbons in automotive air conditioners. In the present study, the main concern is to obtain experimental results from the use of different ratios of hydrocarbon mixtures as a replacement refrigerant in automotive air conditioners working with HFC-134a. The experimental study is conducted at various mixture ratios with the same air conditioner. Finally, the most appropriate mixture of hydrocarbons as an alternative refrigerant to HFC-134a is proposed.