# Experimental Study of Methane Combustion Efficiency in a High-Enthalpy Oxygen-Containing Flow
## 2 Experimental Facility and Data Processing Technique  
Taking into account the multistage nature of physical and chemical processes, it is advisable to study the efficiency of methane combustion in a HOF using a facility with oxidative reactions realization in a constant cross-section channel [53; 54]. In this study, the tests were carried out on an experimental facility, the scheme of which is shown in Figure 1. The experimental facility consists of a heat exchanger (1), a rectifying element (2), a crossover joint (3), the methane supply pylons (4), a constant cross-section channel (5), a throttler (6), and a longitudinal force sensor (7). The facility has five static pressure sampling points (8), a static pressure sampling point for fast processes registration (9), and the temperature measurement point (10) for the HOF enthalpy determination. Let us consider the operating principle of the experimental facility. The oxygen-containing flow (air) passing through the duct of the ohmic type heat exchanger (1) heats to the required enthalpy values. After the heat exchanger, the high-enthalpy oxygen-containing flow (HOF) passes through the rectifying element (2) and the crossover joint (3) to ensure the uniformity of the velocity, pressure and temperature fields at the input to the constant cross-section channel (5). The rectifying element is made on the honeycomb straightener principle with a characteristic transverse cell size of 5 mm and a length of 20 mm. The channel (5) has a square cross-section with an area of 0.01 m\({}^{2}\) and 10-fold elongation. The structural elements (pylons) with fuel injectors (4) with a diameter of \(\sim\)0.8 mm, distributed evenly over the channel cross-section, are installed at the channel inlet. The relative number of injectors corresponds to 1600 m\({}^{-2}\). The methane is supplied through the injectors, which ignites and combusts after its mixing with the high-enthalpy oxygen-containing flow. The ignition occurs using an electric-spark plug. At the outlet the throttler (6) is installed with an equivalent flow area of 3.9 \(\times\) 10\({}^{-3}\) m\({}^{2}\), which is necessary to ensure the required velocity and pressure in the constant cross-section channel. The sensor (7) records the force generated by the output pulse of the methane combustion products flow with the HOF. The static pressure registration was carried out by strain transducers with a frequency of 100 Hz. The measurement error is not more than \(\pm\)0.25% of the upper measurement range. To measure pressure pulsations, high-frequency piezoelectric sensors with an operating frequency range of up to 200 kHz were used. The signal from the sensors was received to the recorder-analyzer input, which allows to conduct real-time measurements and express analysis of pressure pulsations. The registration of pressure pulsation signals was carried out at a frequency of \(\sim\)13.5 kHz, which made it possible to carry out frequency analysis in the range (0,..., 6.75) kHz. One of the most significant indicators of the workflow efficiency is the combustion completeness coefficient [55]. Taking this into account, an important aspect of the methane combustion study in constant cross-section channel is the indirect measurement of the combustion completeness coefficient \(\eta\). In this study, we used the approach which was previously described in [54]. Figure 1: Experimental facility scheme. 1—heat exchanger; 2—rectifying element; 3—crossover joint; 4—methane supply pylons; 5—channel of constant cross–section; 6—throttler; 7—longitudinal force sensor; 8—static pressure sampling points; 9—pressure pulsations sampling point; 10—HOF temperature measurement point. The constant cross-section channel receives the HOF mass flow rate Ga and the methane mass flow rate Gf.