## 1 Introduction
According to experimental results, LPG and only AHC blended fuels increased the NOx emission compared to diesel fuel operation. Experimental result showed that the thermal efficiency of LPG powered diesel engine was comparable to pure diesel fuel operation. In terms of exhaust emissions, the NOx and smoke could be considerably reduced with using the various blend of LPG, DTBP, and AHC. [PERSON] [21] focused on the effect of propane ratio changes in LPG content on emissions and performance in dual-fuel diesel engines. In the study, LPG with various propane contents was delivered to a diesel engine with EGR capability. The best engine efficiency was achieved with a 40% propane ratio. Depending on the LPG content, high butane ratio led to the decreasing of NOx emissions and high propane content caused the reduction of CO emission as well. In a mixture of 30% butane and 70% propane content, the engine performance remained at the same level as pure diesel fuel. NOx emissions were reduced about 27% at full load in 70% propane and 30% butane mixture. [PERSON] et al. [30] conducted a performance evaluation of a diesel/LPG dual fuel engine. 10%, 20%, 30%, 40% and 50% of LPG were sent to intake manifold of the single-cylinder test engine. Experiments were carried out at constant 1500 rpm engine speed at different loads. The 50% LPG fuel ratio could only be used up to 40% of the engine load. In all LPG fuel mixture ratios, the effective efficiency had increased when it was compared with pure diesel fuel. They proved that smoke emission and specific fuel consumption were reduced gradually while the LPG ratio of fuel mixture was increasing. [PERSON] and [PERSON] [31], studied the usage of LPG in the diesel engines experimentally. They used an LPG injector mounted in the intake manifold. The measurements were performed in 10%, 20% and 25% LPG ratios. The maximum improvements in engine power, engine torque, and specific fuel consumption were achieved with 25% LPG ratio. In terms of exhaust emissions, NO\({}_{\rm x}\) and HC emissions decreased with all LPG ratios while CO and CO\({}_{2}\) emissions increased. [PERSON] et al. [32], investigated the influence of hydrogen and LPG addition on the efficiency and emissions of a dual-fuel diesel engine. They showed that the efficiency was increased with the usage of LPG at high loads while HC, NO\({}_{\rm x}\), and smoke emissions were reduced. They observed a serious knocking in the test engine at the 70% LPG ratio. The best engine performance was obtained at 40% LPG ratio. [PERSON] et al. [33] studied on the diesel/LPG dual fuel engine. The gas phase LPG fuel was delivered to the intake manifold of a single-cylinder diesel engine. The experiments were carried out at 50% engine load and constant 1500 rpm engine speed. Experimental results were recorded at 35%, 67%, 73% and 90% LPG fuel ratio approximately. As the LPG fuel ratio increased, NO\({}_{\rm x}\) emissions decreased, and HC emissions increased regularly. Additionally, CO emissions increased at first and then decreased slightly. It was seen that there was a slight decrease in the cylinder pressure due to the increase in the LPG fuel ratio. LPG in the liquid phase is mixed with diesel fuel and delivered to the high-pressure pump when the liquid phase LPG fuel is used in diesel engines. The mixture of liquid LPG and diesel fuel is injected into the cylinder with the diesel injector at high pressure. The liquid phase LPG can change to the gas phase easily when it is injected into the cylinder because of the low boiling point of LPG. The quick evaporation of the LPG in diesel/LPG blend can improve the atomization of the fuel spray. The increase of LPG content in the fuel blend will decrease the cetane number of diesel/LPG blend, and this will lead to the increase of ignition delay. In addition, the latent heat of evaporation and the Lower Heating Value (LHV) of diesel/LPG blend give a slight increase in ignition delay.