## 2 Experiment Description
### 4-Equations for Calculation of the Unadjusted and Adjusted Fuel Consumption  
Figure 4 demonstrates the flow chart of fuel consumption equations. This flow chart indicates how each of fuel consumption equations are related with each other. Table 3 shows the one unadjusted and three adjusted fuel consumption equations. Equation (A) which calculates the unadjusted fuel consumption is divided into two processes. The first step is to obtain each emission concentration of HC, CO, and CO\({}_{2}\), through Equation (a) required for mass of emission discharged during a specific stage of one cycle. Next, the concentrations of each emission calculated through Equation (a) and characteristics of fuel are substituted into Equation (b). Then, unadjusted fuel consumption for LPG can be produced for each 5-driving cycles. The reason why the equation is called an unadjusted fuel efficiency formula is that no adjustment factors are applied. Also, it should be noted that Equation (b) is only applied to vehicles that are fueled by LPG. The first Equation (B), of three adjusted fuel consumption equations had been used until 2007. The Equation B for fuel consumption of city and highway mode demand for fuel efficiency were obtained from Equation A measured during the FTP and HWFET driving cycle. Then, each of its values was multiplied by the adjustment factor, 0.9 and 0.75, to produce adjusted fuel consumption of city and highway modes. Next, the second equation, Equation (C), was developed to approximate real world fuel consumption by implying fuel economy results obtained from Equation (A) measured during 5-cycle tests, characterized with various external atmospheric conditions and driving environments. Fuel efficiency results that were measured during US06, SC03, and cold FTP driving cycles calculated from Equation A were put into the Equation (C) for each city and highway mode, making it possible to consider each characteristic that the three driving cycles contain. Each of the three cycles, US06, SC03, and cold FTP, are characterized by the presence of frequent acceleration and deceleration regions, driving a car with the air conditioning system operating, and the condition of cold atmosphere temperature. Fuel efficiency value of city and highway modes obtained from Equation (C) measured with diverse vehicles, regardless of the types of fuel used in the vehicles, can be used for making linear interpolations for city and highway modes. Then, slopes and intercepts that were obtained from linear interpolations are used for making D fuel consumption equations of city and highway modes. So, each fuel consumption value for these two modes accounting for various driving environments can be conveniently obtained without going through the complex process shown in Equation (C). These three correction formulas (B-D) can be used, regardless of fuel used. However, since fuel consumptions are measured in compliance with the carbon balance method that emitted gases comprised of carbon element are used for estimating fuel economy measured with the vehicle placed on the chassis dynamometer and driving along the driving cycles, it is limited in perfectly reflecting conditions shown on the real-road on fuel consumption that are calculated from adjusted fuel consumption equations. Figure 4: Flow chart of fuel consumption equations. \begin{table}
\begin{tabular}{c c} \hline \hline
**Case** & **Equations for Fuel Consumption** \\ \hline \multirow{7}{*}{A} & (a) Total exhaust gas concentration for HC, CO and CO\({}_{2}\) measured during the FTP cycle. \\  & **Yvnn = 0.43\(\times\)Yct +Ys+Dct +Dbs + 0.57\(\times\)[Tht+Ys+Dht+Dbs]** \\  & (b) Fuel efficiency for the vehicle powered by LIG.