# Experimental Study of Methane Combustion Efficiency in a High-Enthalpy Oxygen-Containing Flow
## 3 Experimental Results and Their Analysis  
The studies were carried out for the range of HOF initial enthalpies \(H\) = 350,..., 700 kJ/kg. Four modes were selected and for each of them the fuel excess coefficient \(\varphi\) was varied in the range from 0.5 to 1.0. The pressure in the constant cross-section channel did not exceed 0.5 MPa in each of the modes, and the flow ratio to the channel area varied in the range from 130 to 140 kg/(s\(\cdot\)m\({}^{2}\)) depending on the test mode. The tests were carried out according to the test sequence diagram shown in Figure 2, which represents the dependence of the longitudinal force sensor readings (R) on time (t). At the t1 section of the test sequence diagram, the experimental facility output to a given mode is shown, heating of the HOF in a heat exchanger to a given temperature. At the t2 section, methane is supplied, which ignites and combusts in a constant cross-section channel. A sharp increase in the longitudinal force sensor readings is observed in this area. At the t3 section, the methane supply is completed and combustion stops. This process is accompanied by a sharp drop in the longitudinal force sensor readings and the HOF supply to the experimental facility stops. Figure 2: Test sequence diagram. Figure 3 represents the dependence of the reduced pressure \(p^{\prime}\), which is equal to the ratio of static pressure along the duct of constant cross-section channel \(p\) at the moment before the methane supply in the constant cross-section channel during the combustion of HOF and methane mixture to the maximum static pressure, realized during combustion from the reduced length of the constant cross-section channel \(L^{\prime}\) on one of the test modes. As a result of the experimental data processing, the dependences of the combustion completeness coefficient on the fuel excess coefficient were obtained for different initial HOF enthalpies. The results are shown in Figure 4.  
Figure 4: Dependence of the combustion completeness coefficient on the fuel excess coefficient. 1—\(H\) = 360 kJ/kg; 2—\(H\) = 490 kJ/kg; 3—\(H\) = 580 kJ/kg; 4—\(H\) = 690 kJ/kg; 5—the data from the study [48] where H \(\approx\) 580 kJ/kg. Figure 3: Dependence of the reduced pressure on the reduced length. 1—without combustion; 2—with combustion; 3—static pressure sampling point. The graph depicts the approximated dependences based on the obtained experimental data. As can be seen, with an increase in the initial HOF enthalpy, the combustion completeness coefficient increases and with an increase of the fuel excess coefficient, a monotonic increase in \(\eta\) to the some maximum is first observed. With a further decrease in \(\varphi\), \(\eta\) begins to decrease as well. For comparison, the graph also shows some of the results from the study [48], which correlate fairly well with this study data. The differences in the combustion efficiency coefficients by 3-4% are due to the fact that the experiments in study [48] were carried out with not only air heating, but also a methane heating. In addition, in the current study, a constant cross-section channel was considered, and in study [48]--a channel with ledges, behind which recirculation zones are formed that stabilize combustion. It is worth noting that an increase in the enthalpy of the oxygen-containing oxidizer to 690 kJ/kg allows one to surpass the results previously published in study [48] without using additional measures to stabilize combustion, which leads to total pressure losses. Figure 5 shows the dependence of the maximum values of combustion completeness coefficient \(\eta_{max}\) on the initial enthalpy and the dependence of the combustion completeness coefficient \(\eta_{-1}\) on the initial enthalpy with fuel excess coefficient equal to \(\varphi=1\). In the general case, an increase in enthalpy, as stated above, leads to an increase in the combustion completeness coefficient.