Unified length scale of spray structure by unlike impinging jets

Off-Design Combustion in Liquid-Propellant Rocket Engine with High-Frequency Instability

Experimental Validation of Off-design Combustion for Liquid-propellant Rocket Engine High-frequency Instability

The high frequency instability of a JP-4 fuel and liquid oxygen rocket combustor, especially the effects of this instability on heat transfer augmentation to the chamber wall, was studied. The FOF triplet type injector element and two chambers with different lengths were used in the experiments. Both chambers delivered a 10kN thrust at a 3.5MPa chamber pressure. The pressure oscillation generated spontaneously was identified as being a longitudinal first mode. The ratio of rms pressure amplitude to average chamber pressure observed in unstable combustion was 0.23 at most. In order to obtain stable combustion or weak unstable combustion, a damping device based on Crocco’s theory of longitudinal high frequency instability was designed and used successfully. The heat flux to the wall increased six to seven times at most due to the instability. It was shown that the increase of the bulk heat transfer coefficient was proportional to the square root of rms pressure amplitude when the effective temperature, based on the frequency of oscillation, was used. Various considerations, including the effect of solid carbon particles, suggests that Dent’s model of convective heat transfer augmentation is more reasonably consistent with the experimental results than is Hanby’s model. The time average static pressure along the chamber axis increased downstream after it had first decreased. Theoretical analysis of the periodically oscillating one-dimensional flow showed reasonable agreement with the experimental results.

High Frequency Instability in a Lox-Kerosene Rocket Combustor (Effects on Heat Transfer Augmentation)

The injection and combustion characteristics of unlike-impinging triplet injector for JP4 fuel and liquid-oxygen rocket combustor were studied. The injector element types considered were the OFO type, which consists of two outer oxidizer jets and one central fuel jet, and the FOF type, which consists of two fuel jets and one oxidizer jet. The spray characteristics of typical single elements of the two types were investigated through cold flow tests. Based on these tests, three multiple-element injectors (20 and 40 elements, 10 kN thrust at 2 MPa chamber pressure) were designed and fabricated, and were evaluated by means of cold flow tests and firing tests with combustion chambers of various lengths. The results were compared with a theoretical analysis based on a vaporization model. The conclusions of the study are as follows: 1)The design correlation of orifice area ratio for maximum mixing efficiency was confirmed for both OFO and FOF type elements. 2)The OFO element showed wider spray angles and relatively more uniform mixture ratio distributions than the FOF element. The spray characteristics of the single elements were sensitive to a change in mixture ratio. However, multiple element injectors were insensitive to such a change and showed substantially similar mixing measures, suggesting a marked averaging effect due to mixing with adjacent elements. 3)Since the statistical frequency of mixture ratio for multiple element injectors is approximately expressed by the logarithmic normal distribution function, the measure of mixing can be evaluated in terms of the logarithmic standard deviation or the dispersion, and Rupe’s mixing factor, Em, can be correlated with the mixing C efficiency. 4)Initial droplet diameters of the injectors at several mixture ratios were estimated from the comparison of the experimental performance with the theoretical analysis. The estimated diameters indicate that the vaporization of fuel is the rate controlling process. 5)OFO type injectors showed higher performances than FOF types; however, the former gave higher heat flux to the chamber wall. 6)Although direct ignition by a spark plug was used in the study, an injection of a small amount of nitrogen gas into the fuel line was remarkably effective in avoiding hard starts.

文衛小野

Papers

High Frequency Instability in a Lox-Kerosene Rocket Combustor (Effects on Heat Transfer Augmentation)

Injection and Combustion Characteristics of Unlike-Impinging Triplet Injector for LOX-Kerosene Rocket Combustor

文衛 小野

Papers

High Frequency Instability in a Lox-Kerosene Rocket Combustor (Effects on Heat Transfer Augmentation)

Injection and Combustion Characteristics of Unlike-Impinging Triplet Injector for LOX-Kerosene Rocket Combustor

文衛小野