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Abstract(s)
A recuperação do conceito de propulsão pulsojato, pontualmente utilizado durante a Segunda
Guerra Mundial, parece estar a conquistar, nos dias de hoje, um novo interesse no meio
aeronáutico. O elevado ruído, bem como as vibrações excessivas características deste tipo de
propulsão, conduziram a que a aplicação no meio aeronáutico civil viesse a ser abandonada. No
entanto, a ausência total ou parcial de partes móveis, a facilidade e baixo custo de produção,
têm direcionado a implementação do pulsojato para o mercado dos Veículos Aéreos Não
Tripulados (UAV’s). Apesar de esta ser uma tecnologia com bastantes anos, ainda restam
dúvidas quanto à operação e desempenho dos pulsojato, por este motivo, ainda são necessários
estudos que desmistifiquem o funcionamento destes motores. No sentido de dar continuidade
ao estudo numérico do dimensionamento de um motor pulsojato sem válvulas, realizado no
Departamento de Ciências Aeroespaciais da UBI, a presente dissertação pretende proceder à
construção física do modelo simulado numericamente, bem como avaliar o seu desempenho,
através da realização de ensaios estáticos. O estudo experimental demonstrou, após exaustivas
tentativas, ser necessário um aumento de 18,5 cm do ducto de escape, de forma a permitir o
efeito pulsante autossustentável e, além disso, uma adição de 4,7 cm no ducto de admissão,
no sentido de torná-lo acelerável. Esta investigação permitiu perceber também, a importância
do divergente instalado sobre a tubeira de escape, pois sem este componente a combustão
autossustentada não se verifica. De forma a testar o comportamento do pulsojato em diferentes
cenários, sete caudais mássicos de propano foram injetados ao longo do ducto de admissão:
1,4, 1,8, 3,3, 3,9, 4,6, 7,1 e 7,7 g/s. Para cada um dos testes, foram gravados os dados relativos
à tração, temperatura da admissão, escape e câmara de combustão, frequência e nível de
pressão sonora. A tração estática máxima produzida pelo pulsojato foi de 26,14 N, superando
os 24,80 N obtidos nas simulações numéricas, ainda assim, este valor ficou aquém dos 58,90 N
idealizados para o motor. A frequência operacional do pulsojato sem válvulas variou de 111 a
125 Hz, consoante o caudal mássico injetado. Durante os testes experimentais verificou-se que,
mesmo com dois reservatórios de propano em paralelo e com acelerador totalmente aberto, a
combustão autossustentada no interior do pulsojato permaneceu ativa. Isto indicia que, se
caudais mais elevados fossem testados, a força de tração seria, eventualmente, amplificada.
The recovery of the pulsejet propulsion concept, widely used during World War II, seems to be winning nowadays a new interest in aeronautical environment. The high noise and excessive vibrations, characteristic of this type of propulsion, led to the separation from civil aviation. However, the possibility of having no moving parts, a very simple construction and a low cost, have driven the implementation of pulsejet to the Unmanned Aerial Vehicles (UAV’s) market. Although this technology has been developed many years ago, operation and performance of pulsejets is still not fully understood. For this reason, studies are required to explain the operation of these engines. In order to continue the numerical study of design of a valveless pulsejet engine, carried out at UBI Aerospace Science Department, this dissertation intends to manufacture the virtual model, as well as evaluate its performance through static runs. The experimental study showed, after exhaustive attempts, that 18.5 cm of the exhaust duct should be added in order to allow the self-sustaining pulsating effect, and 4.7 cm to the intake duct, in order to make it throttleable. This investigation also allowed to understand the importance of the flare installed on the exhaust nozzle, since without this component self-sustained combustion does not occur. In order to test the valveless pulsejet behavior in different scenarios, seven propane flow rates were injected along the intake duct: 1.4, 1.8, 3.3, 3.9, 4.6, 7.1 and 7.7 g/s. For each run, data acquisition included thrust recording, inlet temperature, exhaust temperature, combustion chamber temperature, operational frequency, and sound pressure level. The maximum static thrust produced by the engine was 26.14 N, exceeding the 24.80 N obtained in numerical simulations. Unfortunately, the 58.90 N expected for the engine was not reached. The operating frequency of valveless pulsejet ranged from 111 to 125 Hz, depending on the injected mass flow rate. During the experimental tests it was found that even with two propane tanks and full throttle condition, self-sustaining combustion remained active. This indicates that if higher flow rates were tested, thrust would eventually be increased.
The recovery of the pulsejet propulsion concept, widely used during World War II, seems to be winning nowadays a new interest in aeronautical environment. The high noise and excessive vibrations, characteristic of this type of propulsion, led to the separation from civil aviation. However, the possibility of having no moving parts, a very simple construction and a low cost, have driven the implementation of pulsejet to the Unmanned Aerial Vehicles (UAV’s) market. Although this technology has been developed many years ago, operation and performance of pulsejets is still not fully understood. For this reason, studies are required to explain the operation of these engines. In order to continue the numerical study of design of a valveless pulsejet engine, carried out at UBI Aerospace Science Department, this dissertation intends to manufacture the virtual model, as well as evaluate its performance through static runs. The experimental study showed, after exhaustive attempts, that 18.5 cm of the exhaust duct should be added in order to allow the self-sustaining pulsating effect, and 4.7 cm to the intake duct, in order to make it throttleable. This investigation also allowed to understand the importance of the flare installed on the exhaust nozzle, since without this component self-sustained combustion does not occur. In order to test the valveless pulsejet behavior in different scenarios, seven propane flow rates were injected along the intake duct: 1.4, 1.8, 3.3, 3.9, 4.6, 7.1 and 7.7 g/s. For each run, data acquisition included thrust recording, inlet temperature, exhaust temperature, combustion chamber temperature, operational frequency, and sound pressure level. The maximum static thrust produced by the engine was 26.14 N, exceeding the 24.80 N obtained in numerical simulations. Unfortunately, the 58.90 N expected for the engine was not reached. The operating frequency of valveless pulsejet ranged from 111 to 125 Hz, depending on the injected mass flow rate. During the experimental tests it was found that even with two propane tanks and full throttle condition, self-sustaining combustion remained active. This indicates that if higher flow rates were tested, thrust would eventually be increased.
Description
Keywords
Motor de Deflagração Por Pulsos. Propano Pulsojato Pulsojato Não Valvulado Pulsojato Tipo Chinese