Blast Compression Intake proposed design
Posted: Mon Jan 24, 2005 11:13 am
I am moving part of my latest post in the CC design thread to a new thread for seperate discussion. This is my proposed design for generating blast compression and transverse waves to compress the CC and initiate ignition timing under designer control limiting the requirements for precise resonance timing.
I am designating the term BCI to represent my "Blast Compression Intake" assembly. They are designed to be used in a thermojet configuration PDE or pulsejet. See my "Proposed CC Design" thread.
The BCI is designed to be used in the place of a normal intake tube. It consists of a lenght of straight small diameter tube that runs parallel to the exhaust tube with a T intersection that is the actual separate intake tube of very short lenght with a flared end.
Multiple BCI tubes should be angled into the CC to converge the blast fronts to intersect at the chosen ignition point in the CC. Since it angles into the CC, it needs to be bent so it can run parallel to the exhaust tube. This bend is actually beneficial, it will induce rotation (like the currents in a meandering river) in the exhaust gasses providing a small tornado of hot gases into the CC. This will cause rapid widespread combustion in the CC.
BCI tubes should be a little longer than the exhaust with a conical end plug to compress, ignite a fuel mixture there. The timing for the reflective shockwave should arrive at about the correct time for reigntion of follow on cycle. The "actual" intake will have to be split off from these Blast compression tubes ~1/4 of the way from the CC to the end plug. This short intake tube will be closest to the CC end of the BCI.
I envission the intakes coming in at 90 degrees off this tube and curved to run parallel to it. The curve is required to induce vortex rotation to draw mixture in faster. It will be required because the intake must navigate a 90 degree turn into the BC tube when recharging the dead end branch or refreshing the CC. This intake tube needs to be short. It will need a high resonance frequency. The waves from its oscilation should not really propogate back into the CC due to the 90 degree intersection. This oscilation will operate like a high speed pump.
Theory of Operation:
The CC ignites, drives shockwave down both the exhaust and the BCI tubes. The wave in the BCI tube will pass the intake port at ~1/4L position. This will vent some of the back pressure but the initial shockwave will not make the 90 degree turn and momentum of the exhaust gasses will carry alot of the expasion gassed straight down to the dead end of the BCI tube.
The shockwave will compress the mixture in the BCI tube dead end, reflect off the conical end-cap (focusing the wave) and drive the mixture directly into the flamewave that followed the shockwave. Whether this mixture ignites by the shockwave focusing alone or ignites when the flamewave intersects is basicly irrelevant. This charge has only 1 exit path, back towards the CC.
By the time the enhanced reflected blast is starting to return, the CC will be at its low pressure point sucking in mixture thru the intake. This is due to the fact that the BCI is longer then the exhaust tube. The very short intake tube branched from the BCI will be resonating at a high frequency pumping multiple layers of mixture into the top (CC end of the BCI) and being drawn into the CC. The top 1/4 section of the BCI should also be close to vacuum due to overexpassion by gas momentum.
One reason Im using 3 to 5 intakes thermojet style is to allow enough intake volume during this reduced timeframe for recharging the CC. The other reason is to drive the intake mixture into the closed dead end of the CC frontwall.
The reflected blast from the BCI driven by the small secondary combustion in the dead end of the BCI will drive pass the intake port blocking it. It will vent some of its back pressure but the majority of the flow should be driving into the CC due to momentum and the lower pressure in the CC.
At this same time, the reflectioned waves from the main exhaust tube will be drawing in the fresh cold air mass from the exhaust driving up the CC pressure. The BCI shockwave will DRIVE the remaining mixture still in the top 1/4 of the tube into the CC compressing it into the nose-cone with a flamewave following right behind it.
Once the BCI overexpands, a fresh mixture is drawn from the intake refreshing the BCI dead end section. This is occuring while 3-5 transverse blast waves intersect into the CC at the ignition point into a mass of highly compressed layers of mixture with a flame front driving right behind it thus reigniting the CC.
Resonance timing from the exhaust reflections do not have to be timed to intersect perfectly. There should be no need for exact timing. The BCI blast front should be plenty of energy to reignite the CC. As long as the cold air mass has been reloaded into the exhaust tube. That and helping to overpressurize the CC is all that is needed from the exhaust reflections.
This set up should provide much higher CC compression. It should provide layers of mixture drawn into the CC all compressed into the dead end nose cone of the CC.
The only problems I forsee are being able to draw in enough mixture during the shortened refresh cycle thus the need for multiple intakes and the vortex induced by curving the short intake tube. This has the added benefit of providing transverse intersecting wavefronts. Another forseeable problem would be from timing but the ignition timing can be varied by moving the BCI conical end plug closer towards the CC. The final problem will be preventing the entire thing from reaching DDT by the high compression in the CC or BCI dead ends when used in a pulsejet of limited tube thinkness.
I got my inspiration from Bruno's BCVP (Thanks Bruno). But I see several problems with his proposal. The intake and exhaust have to share the same tube. The BC is not driving into a dead end, therefore it is much harder to get good compression. His design is also just a long narrow CC that doesnt have time to refresh. By placing the intake between the blast from a large CC and a small dead end reflection and splitting the BC into multiple smaller chambers as well as providing a clear separate path for exhaust has helped to solve those issues.
One other thing I would like to point out. If the BCIs dont allow the CC to breath enough, you could also use some normal Intake tubes. For example: a 5 intake port thermojet with 2 normal intake tubes and 3 BCI tubes configured in a star configuration or 6 ports of 3 and 3 in a hexagonal configuration.
I am designating the term BCI to represent my "Blast Compression Intake" assembly. They are designed to be used in a thermojet configuration PDE or pulsejet. See my "Proposed CC Design" thread.
The BCI is designed to be used in the place of a normal intake tube. It consists of a lenght of straight small diameter tube that runs parallel to the exhaust tube with a T intersection that is the actual separate intake tube of very short lenght with a flared end.
Multiple BCI tubes should be angled into the CC to converge the blast fronts to intersect at the chosen ignition point in the CC. Since it angles into the CC, it needs to be bent so it can run parallel to the exhaust tube. This bend is actually beneficial, it will induce rotation (like the currents in a meandering river) in the exhaust gasses providing a small tornado of hot gases into the CC. This will cause rapid widespread combustion in the CC.
BCI tubes should be a little longer than the exhaust with a conical end plug to compress, ignite a fuel mixture there. The timing for the reflective shockwave should arrive at about the correct time for reigntion of follow on cycle. The "actual" intake will have to be split off from these Blast compression tubes ~1/4 of the way from the CC to the end plug. This short intake tube will be closest to the CC end of the BCI.
I envission the intakes coming in at 90 degrees off this tube and curved to run parallel to it. The curve is required to induce vortex rotation to draw mixture in faster. It will be required because the intake must navigate a 90 degree turn into the BC tube when recharging the dead end branch or refreshing the CC. This intake tube needs to be short. It will need a high resonance frequency. The waves from its oscilation should not really propogate back into the CC due to the 90 degree intersection. This oscilation will operate like a high speed pump.
Theory of Operation:
The CC ignites, drives shockwave down both the exhaust and the BCI tubes. The wave in the BCI tube will pass the intake port at ~1/4L position. This will vent some of the back pressure but the initial shockwave will not make the 90 degree turn and momentum of the exhaust gasses will carry alot of the expasion gassed straight down to the dead end of the BCI tube.
The shockwave will compress the mixture in the BCI tube dead end, reflect off the conical end-cap (focusing the wave) and drive the mixture directly into the flamewave that followed the shockwave. Whether this mixture ignites by the shockwave focusing alone or ignites when the flamewave intersects is basicly irrelevant. This charge has only 1 exit path, back towards the CC.
By the time the enhanced reflected blast is starting to return, the CC will be at its low pressure point sucking in mixture thru the intake. This is due to the fact that the BCI is longer then the exhaust tube. The very short intake tube branched from the BCI will be resonating at a high frequency pumping multiple layers of mixture into the top (CC end of the BCI) and being drawn into the CC. The top 1/4 section of the BCI should also be close to vacuum due to overexpassion by gas momentum.
One reason Im using 3 to 5 intakes thermojet style is to allow enough intake volume during this reduced timeframe for recharging the CC. The other reason is to drive the intake mixture into the closed dead end of the CC frontwall.
The reflected blast from the BCI driven by the small secondary combustion in the dead end of the BCI will drive pass the intake port blocking it. It will vent some of its back pressure but the majority of the flow should be driving into the CC due to momentum and the lower pressure in the CC.
At this same time, the reflectioned waves from the main exhaust tube will be drawing in the fresh cold air mass from the exhaust driving up the CC pressure. The BCI shockwave will DRIVE the remaining mixture still in the top 1/4 of the tube into the CC compressing it into the nose-cone with a flamewave following right behind it.
Once the BCI overexpands, a fresh mixture is drawn from the intake refreshing the BCI dead end section. This is occuring while 3-5 transverse blast waves intersect into the CC at the ignition point into a mass of highly compressed layers of mixture with a flame front driving right behind it thus reigniting the CC.
Resonance timing from the exhaust reflections do not have to be timed to intersect perfectly. There should be no need for exact timing. The BCI blast front should be plenty of energy to reignite the CC. As long as the cold air mass has been reloaded into the exhaust tube. That and helping to overpressurize the CC is all that is needed from the exhaust reflections.
This set up should provide much higher CC compression. It should provide layers of mixture drawn into the CC all compressed into the dead end nose cone of the CC.
The only problems I forsee are being able to draw in enough mixture during the shortened refresh cycle thus the need for multiple intakes and the vortex induced by curving the short intake tube. This has the added benefit of providing transverse intersecting wavefronts. Another forseeable problem would be from timing but the ignition timing can be varied by moving the BCI conical end plug closer towards the CC. The final problem will be preventing the entire thing from reaching DDT by the high compression in the CC or BCI dead ends when used in a pulsejet of limited tube thinkness.
I got my inspiration from Bruno's BCVP (Thanks Bruno). But I see several problems with his proposal. The intake and exhaust have to share the same tube. The BC is not driving into a dead end, therefore it is much harder to get good compression. His design is also just a long narrow CC that doesnt have time to refresh. By placing the intake between the blast from a large CC and a small dead end reflection and splitting the BC into multiple smaller chambers as well as providing a clear separate path for exhaust has helped to solve those issues.
One other thing I would like to point out. If the BCIs dont allow the CC to breath enough, you could also use some normal Intake tubes. For example: a 5 intake port thermojet with 2 normal intake tubes and 3 BCI tubes configured in a star configuration or 6 ports of 3 and 3 in a hexagonal configuration.