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This paper presents the environment-friendly mixture compositions of hydrocarbons (HC)- and hydrofluorocarbon (HFC)-based ternary mixtures that can be better alternatives for R134a in domestic refrigeration units. Combustible refrigerant HCs (R290, R600, R600a) and HFCs (R152a and R161) are used along with the dilutants R13I1, R245fa, R134a, R227ea, and R125 and their flammability studies were carried out theoretically. Minimum inerting concentration (MIC) is used to classify the flammable and non-flammable zones of the ternary mixtures. MIC points estimated with modified thermal balance method (MTBM) are compared with 62 experimental data points available in the literature. It was calculated that MTBM predicted the MIC values with in ±9%, for most of the working fluids selected in this study. R13I1 is used along with all the refrigerant (HC and HFC) combinations (as the first dilutant) while the effect of other dilutants on the system performance is carried out theoretically. It is predicted from the flammability diagram (developed in this study) that the inert effect of R227ea is higher than of R245fa, R134a, and R125. It is also observed that the drop in coefficient of performance (COP) is significant with R290/R13I1/R245fa (with increase in R245fa) mixture when compared to other combinations. Finally, mixtures R600a/R13I1/R245fa, R600a/R13I1/R227ea, R600a/R13I1/R134a, R600a/R13I1/R125, R161/R13I1/R134a, R290/R13I1/R125, R161/R13I1/R227ea, and R161/R13I1/R125 are identified as the best environment-friendly mixture compositions as alternatives to R134a. It is also calculated that the mixture R600a/R13I1/R125 possesses COP greater than 10% to R134a at the same working conditions.

R1234yf is considered as a better alternative for R134a (the conventional refrigerant) due to its low global warming potential value, while its usage is limited because of its flammability. The flammability of any flammable refrigerant can be reduced by adding dilutants that are inert. Two methods (group contribution method and thermal balance method) were used to estimate the minimum inerting concentration (which decides the flammability zone) of the binary mixtures (refrigerant + dilutant). It was observed that the group contribution method and the thermal balance method predicted minimum inerting concentration of the refrigerant mixture (refrigerant + dilutant) with an absolute error of more than 50% and 8%, respectively. Therefore, a modified thermal balance method is proposed in this study to estimate the minimum inerting concentration and found that the proposed method predicts the values with reasonable accuracy when compared with the available experimental data. Further, the minimum inerting concentration for the dilutants R125 and R245fa (that are not experimentally known) with R1234yf is estimated. The results indicated that R227ea has better inert effect with R1234yf when compared to other dilutants (R125, R134a and R245fa) considered in this study. It was also found that the critical inerting concentration for R1234yf is 36.5%.

The present article analyses the refrigerant safety parameters flammability, global warming potential (GWP) and coefficient of performance (COP) for twenty-seven combinations that contain two flammable and one non-flammable (dilutant) component. The flammability of the flammable refrigerants R290, R600, R600a, R152a and R161 were investigated with different dilutants such as R245fa, R13I1 and R134a. To determine the minimum inerting concentration (which decides the flammable zone), two methods were used: thermal balance method (TBM) and the modified thermal balanced method (MTBM). The MICs estimated with both the methods are compared against the 50 experimental data points available in the literature (for different ternary mixtures). It was found that for all the ternary mixtures, majority of the MIC values estimated with MTBM are within ± 8% while with TBM are within ± 30%. Fifty-five ternary mixture compositions were identified (from the proposed twenty-seven mixture combinations) using the MICs predicted by MTBM. The COPs of the identified mixtures M1-M6, M8-M12, M14-M24, M26-M30, M34-M39 and M53-M54 are estimated to be less than 10% of the COP of R134a (at the same operating conditions). It is also estimated that the corresponding GWP value of the mixtures (M1 to M6, M8 to M12, M14 to M24, M26 to M30, M34 to M39, M53 and M54) are reduced by 91 to 99% when compared to R134a (GWP = 1300).

The present energy scenario hydrogen fuel plays a dominant role in the power generation. Due to its unique characteristics of an extensive range of flammability, high flame speed, and diffusivity. In this present investigation, the diesel engine is converted into dual-fuel mode devoid of major conversions of the engine. The tests are performed on a dual-fuel mode and investigated the efficiency, emissions, and combustion features of the diesel engine. In the present context, hydrogen and biogas are injected from the inlet manifold as subsidiary fuel and diesel are injected as pilot fuel. The gaseous fuel injected in two different flow rates they are, 3 litres per minute (lpm), and 4lpm. The results from the experimentation revealed that the diesel with 4 lpm of hydrogen shows the 31.11 % enhancement of brake thermal efficiency but it shows 4.14% higher NOX emissions when compared with the pure diesel. But it shows. At the same time diesel with 4 lpm of Biogas exhibits 15.90% enhancement of brake thermal efficiency and 8.96% decrease in the NOX emissions in contrast to that of the single-mode of fuel with diesel.

The present investigations were carried out on the common rail diesel injection (CRDI) engine in dual-fuel mode with exhaust gas recirculation. Biogas is one of the best alternatives for conventional fuel which has several benefits with limitations. In dual-fuel mode, biogas was injected from the inlet manifold at flow rates of 4 and 5 litres per minute (lpm) as a secondary fuel and diesel was used as the primary fuel. The biogas at 5 lpm consumption gave a 6.78% brake thermal efficiency higher than that of diesel fuel. Exhaust gas recirculation (EGR) was used in dual-fuel mode at a flow rate of 5 lpm of biogas. The use of NOX resulted in a drastic reduction of about 50% for the 5 lpm with 5% EGR when compared with other samples. However, it led to an increase in HC emissions due to lower heat release rate. In dual-fuel mode, the flow rate of 5 lpm produced the highest in-cylinder pressure of 71.1 bars at a crank angle of 366° and lowest in-cylinder pressure for 5 lpm with 5% EGR.