Injector Plate Research Articles

The effect of drop size on emissions from the primary zone of a gas turbine type combustor

Some of the important variables influencing the processes of liquid fuel combustion and pollutant generation are: i) fuel drop size, ii) local equivalence ratio, iii) inlet air temperature, iv) combustor pressure, v) residence time, and vi) recirculation. In order to isolate the effects of these variables a research type combustor has been designed and is now operative. The combustor uses an air-fuel preparation system which allows independent and controlled variation of each of the above variables. A stable flame can be maintained within the combustor without the aid of an artificial flame holder. Pollutant level measurements have been made for the following range of conditions: o i) spray Sauter mean diameter 26–45 μm ii) primary zone equivalence ratio 0.9–1.1 Unheated inlet air was used for these tests with the combustor exhausting into the open atmosphere. The emission samples were extracted at a point 6-1/2 in. from the injector plate along the combustor axis. Results from the measurements made so far show the following trends at the fixed sampling location for decreasing drop size: i) a decrease in the unburned hydrocarbon levels, ii) an increase in CO level at the point of sapling, and iii) a decrease in the mean values of NO concentrations. Mathematical analysis of the emission data successfully predicted the presence of solid carbon for large drops and the lack of same with the smaller drops.

Reply by Authors to P. Katz and to T. Papis

HE comments are concerned with the basic assumption that the gases in the exit plane are rotating with the same angular velocity as the body. In the real vehicle this assumption may not be correct, but an accurate time history of the gas particles is difficult to obtain. The analysis could be modified as indicated by Katz if the rotational velocity were known a priori. It was indicated in both comments that no jet damping would be present for a frictionless gas. The authors' analysis1 would give an upper bound to the effect of jet damping. The mechanism for the transfer of angular momentum between the burned fuel and the vehicle is very complex. For the analysis presented by Warner and Snyder, the needed mechanism could be furnished best by a liquid-propellant rocket. The injector plate of the rocket engine would impart to the fuel some of the angular velocity required for the momentum transfer. A solid-propellant rocket is much easier to model mathematically than the liquid rocket but would rely mainly on the viscous effect of the gas. Papis discussed other effects which could change the spin of the vehicle, and these effects may be greater than the jet damping. The authors are pleased with these constructive comments, for it is through discussions of this nature that knowledge is disseminated.

Rocket Motor Instability Studies

I two previous papers (1, 2), experimental data relating to the problems of combustion instability in 3-in. diam rocket motors were presented. Two types of axial oscillations were identified: (a) A low frequency type of instability (220-360 cps) which is distinguished by abrupt and severe variations in radiation intensity, (b) A high frequency type of instability (600-1500 cps) which corresponds to the propagation of waves longitudinally along the motor. In extreme cases these pressure pulses were transformed into shock waves. In the present paper, additional experimental evidence will be presented relating to these phenomena. All motors were 3-in. ID. Two different injector heads were used: a conventional impinging and a modified impinging (like-on-like type) injector. As described in (1), each injector head uses an injector plate consisting of a series of concentric rings containing drilled injector holes; alternate rings being for fuel and oxidizer. Pairs of liquid jets impinge approximately one inch downstream of the injector plate in the case of the conventional impinging injector, while for the modified impinging head, the impingement point is in the plane of the plate. Table 1 lists details of the injectors. The reactants used in all tests were ethyl alcohol and liquid oxygen.