A proposal for airbreathing hypersonic propulsion.

[exoscientist]

The idea is to bring the hypersonic airstream to a complete stop and use the high temperatures produced to heat hydrogen fuel onboard via efficient heat exchangers. The temperatures reached by re-entry vehicles can be several thousands of degrees. So likewise decelerating the hypersonic air should also result in thousand degree temperatures. There would be no combustion involved in this scenario. <br /> However, it would seem that the best you could do with this would be to break even: you're assuming the kinetic energy of the air with respect to the craft can all be converted to heat, and all this heat can be transferred to the hydrogen then all this heat can be converted back<br />into kinetic flow for propulsion. The last step of course is where big losses would occur.<br /><br />[Note: I've done some preliminary calculations that actually suggest you could get *more* kinetic energy out than the heat energy put in(!) I'm still puzzling over this. Anyone want to address this can take a look at the calculation here:<br /><br />sci.astro /> Proposals for air breathing hypersonic craft. III <br />http://groups.google.com/group/sci.astro/msg/9b74b80d0ad18afd ]<br /><br /> So additionally to this thrust, why not combust the now still air with further hydrogen? I thought of using the very hot hydrogen already heated by the heat exchanger but you want to keep the high exhaust velocity that this achieves, and mixing this with the air reduces this.<br /> To get the highest thrust from the combustion with the air, you would use separate hydrogen for this purpose. Now that the air is still with respect to the craft there is no problem of the fuel and air being at different velocities prior to combustion. And the problem of combusting the fuel with air at temperatures higher than the dissociation temperature of the combustion products will be eliminated<br />since the air will now be cooled by <div class="Discussion_UserSignature"> </div>

 

[willpittenger]

You aren't talking about a straight ramjet are you? They loose effiency at hypersonic speeds. On the other hand, <i>scramjets</i> retain that effiency by <b>not</b> slowing down the airstream. Otherwise, the two are very similar. If you read Challenger Class Shuttle System, you will find I have been working on such concepts for a long time. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[exoscientist]

The difference is that with ramjets and scramjets you are trying to get rid of that heat created by slowing down the supersonic or hypersonic air. I'm suggesting that heat to accelerate the fuel to high velocity.<br /> Scramjets do slow down the air, but from hypersonic to supersonic speeds, not subsonic as do ramjets.<br /> I'll take a look at your proposal, but I must say the choice of name is a little off-putting.<br /><br /><br /> - Bob Clark <div class="Discussion_UserSignature"> </div>