Igniting device fob combustion
US 2447758 A
Description (OCR text may contain errors)
Aug. 24, 1948. LUBBOCK ETAL 2,447,758
v IENITING DEVICE FOR lcomarusron CHAMBERS Fiied Nov. 6. 1942 2 sheets-sheet 1 HHH ug- 24,1948. l. LUBBOCK ErAl. 2,447,758
IGNITING DEVICE FOR COMBUSTION CHAMBERS Filed Nov. 6. 1942 2 Sheets-Sheet 2 IGNITION FLAME .K
INVENToRs (4040 www Aitor/ceq Aug. 24,
UNK l 2,447,758 IGNITING DEVICE Fgg'sCOfBUSTION lz. l;
Isaac Lubbock and Harold James Poole, London,
said Lubbock ossilnor to The Asiatic Petroleum Company, Limited, London, England Application November 8, 1942, Serial No. 484,833
ln Great Britain November 7, 1941 This invention relates to improvements in ignition devices for combustion chambers in which reacting substances, e. g. Ia liquid fuel and a liquid oxidant such as liquid oxygen, are fed so as to burn under pressure, the products of combustion being discharged to an engine or to -a reaction nozzle or the like.
'Ihe object of the invention is to provide a chemical igniter which can be caused to operate practically instantaneously 'and in which the igniting substance, so far as its rate of burning is concerned, will not be seriously influenced by the pressure produced in the combustion chamber. A further object is to ensure that the igniter housing will not be damaged by the subsequent high temperature produced in the combustion chamber.
According to the invention, a hollow igniter body of metal is employed which may be in the form of a. bulb screwed. bolted or otherwise connected to the combustion chamber wall and having a nozzle registering with an oriilce leading to the combustion chamber. Within this body or bulb is accommodated a charge of cordite or similar propellant having the characteristics of burning at an increasing rate with pressure, this charge being ignited inthe conventional manner by means of a primer of powder, fine pellets or strips of the propellant itself. 'I'he firing of the charge is preferably carried out electrically by any of the well known types of electrical fuses or by percussion or friction cap.
The nozzle leading to the combustion chamber is of a size and shape which coupled with the known characteristics of the cordite or propellant charges creates a pressure within the igniter body not less than twice the maximum pressure reached in the combustion chamber upon ignition of the reacting substances. In this way, fromI the well known law of discharge of nozzles against pressures below the critical one of approximately half the higher pressure. the reaction on the rate of burning of the igniterV will be negligible. In
other words, by so designing the nozzle leading from the igniter to the combustion chamber .that 'the'pressure inside the ign-iter is always at least twice the pressure existing in .the combustion chamber, the rate of discharge of gas from the igniter through the nozzle remains constant and the pressure in the combustion chamber has no effect upon therate of burning of the igniter charge and .the pressure produced thereby.
The nozzle may be followed by a somewhat enlarged straight or approximately straight orice in the combustion chamber wall as opposed to an expanding iet so as to create friction and reduce the gas velocity below the maximum obtainable on expansion of the lgni-tlng gases .thus securing as high an ignition temperatureas possible.
'I'he metal body of the lgniter may be lined with an insulating material which may be of any o! the well known refractory types including graphite, but the lining would not be ud where the .time of operation of the combustion chamber is less than that which would give excessive temperatures Within the igniter casing.
The nozzle described above may be made of metal or refractory material, the latter being used lto prevent overheating both during the ignition period and subsequently. A metal inner -tube may be used within any refractory lining to relieve the lining of excessive pressure stresses.
The invention is illustrated by way of example in the accompanying drawing wherein Fig. 1 is a sectional elevation of the ignition device, and Fig. 2 is a somewhat diagrammatic view, partially in section, showing -the ignilter of the present invention ln combination with the combustion chamber of a rocket of known type.
The igniter body which is of metal is shown at i. It is lined with insulation 2 inside of winch is a metal inner tube 3.
The igniter accommodates a charge of cordite I and the head of the ignlter carries a primer 5, above which is the electrical ring means indicated generally at t.
The block of refractory material I in the bottom of the igni'ter is shaped to form the nozzle 8 having a throat followed by an expanding portion,
The ignlter is screwed into the wall 9 of a combustion chamber Il in which a liquid fuel and a liquid oxidant, supplied by a suitable burner i2, are to be burned under pressure.
The nozzle 8 of the igniter is ci' a size and shape which coupled with the known characteristics of the cordite Ycharge creates a pressure within the igniter body not less than twice the maximum pressure reached in lthe combustion chamber upon ignition of the reacting substances.
A straight orifice l0 in the wall 9 of the combustion chamber, which receives the gases issuing from the nozzle 8 and leads them to the combustion chamber, creates friction and reduces the gas velocity below the maximum obtainable on expansion of the igniting gases, thus securing a high ignition temperature.
What we claim is:
1. An ignition device adapted to be secured externally to a combustion chamber in which reactingsubstansareiedsoastoburnimderpres sure and the wall of which has an orince, said device having a body constructed internally to form a space communicating with a nozzle which contracts to a thmat and then merges into an expanding portion. said expanding portion oi the nozzle having its outlet in registry with said oritice, a charge of propellant within said space behind-the nozzle throat, the propellant having the characteristics of burning at an increasing rate with pressure. and means for ring said propellant charge. the sine and shape of said nozzle throat being so designed that the propellant when ignited will create a pressure'withln said body not less than substantially .twice the maximum pressure reached in the combustion chamber upon ignition of the reacting substances.
2. An ignition device adapted to be secured externally to a combustion chamber in which reacting substances are fed so as to burn under pressure and .the wall oi' which has an oriiice, said device having a body constructed internally to form a space communicating with a nozzle which' contracts to a throat and then merges into an expanding portion, said expanding pox-tion of the nozzle having its outlet in registry with said oriiice and said oriilce forming a substantially cylindrical continuation of the nomle having a diameter substantially the same as that oi the outlet end o! the nome. a charge oi propellant within said space behind the nomic throat. the propellant having the characteristics of burning at an increasing rate with pressure. a primer. and means for ilring said propellant charge, the size and shape oi' said noczle lthroat being so designed that .the propellant when ignited will create a pressurev within said body not less than substantially twice the maximum pressure reached in the combustion chamber upon ignition of the reacting substances.
ISAAC LUBBOCK. HAROLD JAMES POOLE.
REFERENCES CITED The following references are of record in the ille of this patent:
UNITED STATES PATENTS