oxygen + benzene bi-propellant rocket engine

[gunsandrockets]

I'm looking for information regarding liquid bi-propellant rocket engines that use oxygen for oxydizer and benzene for fuel.<br /><br />I'm in particular interested in ISP, oxydizer/fuel mixture ratio, and possible problems. Links to relevant information very much wanted too.<br /><br />(Hello Propforce? do you know?)

 

[Boris_Badenov]

I thought this Nomogram had chemical engines, but it doesn't. It's still worth a look. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[billslugg]

gunsandrockets<br /><br />Benzene is a bad carcinogen. Unless you are doing this in interplanetary space be forewarned of the difficulties. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[gunsandrockets]

The potential application is for a rocket engine that uses propellant produced on the surface of Mars from indigenous resources.<br /><br />Since I am not aware of any benzene engine under development or that was ever operational, the fact that benzene is a carcinogen would increase development cost of a new Mars engine.

 

[keermalec]

Kerozene-LOX engines (Delta II or Falcon 1) should have similiar values to a Benzene-LOX engine. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[drwayne]

FWIW, I ran across this...<br /><br />http://marsdrive.com/phpBB2/viewtopic.php?t=436<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[gunsandrockets]

Thanks for looking. I have seen that marsdrive material already and so far it's the best info that I've been able to find. I was hoping to find something in addition to it though...

 

[JonClarke]

Hydrazine is also carcinogenic, and widely used as a fuel. if we can cope with hydrazine, I think we can manage benzene. <br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>I'm looking for information regarding liquid bi-propellant rocket engines that use oxygen for oxydizer and beneze for fuel. <br /><br />I'm in particular interested in ISP, oxydizer/fuel mixture ratio, and possible problems. Links to relevant information very much wanted too. <br /><br />(Hello Propforce? do you know?) <p><hr /></p></p></blockquote><br /><br /><br />Sorry for the late reply. Just noticed the topic.<br /><br />Benzene, C6H6, is a very inert chemical noticeable by its "ring" which wil take a higher energy to break. I'd expect in real life getting it to light would be a challenge and the issue of combustion stability will be tougher than that of LOx & RP-1. Benzene is a little denser in ambient temperature, at 54 lbm/ft^3, this compare to RP-1 at 50.3 lbm/ft^3, means you'll get a little bit of propellant tank volumetric efficiency out of it. Another disadvantage of benzene is its narrow range of temperature between boiling (gas phase) and freezing (solid phase), i.e., between 278.6 deg. K and 353.3 deg. K, a mere 74.7 deg. K range for its liquid phase. So proper thermal control of its temperature will be required.<br /><br />Anyway, here to answer your question. It's highest Isp is at O/F = 2.5 with a theoretical vacuum Isp = 366.1 (assuming Pc = 1,000 psia, and nozzle espsilon= 100).<br /><br />Compare to LOx/ RP-1 at the identical condition, whose vacuum theoretical Isp= 362.4 at O/F = 2.24<br /><br />So a LOx/ C6H6 gets a little higher theoretical Isp (~4 sec) than a LOx/ RP-1, but I think that will be offset by a lower C* efficiency. <br /><br />Another thing, most liquid rocket engines use its fuel to cool its combustion chamber and nozzle. Since benzene has a very narrow liquid phase temperature range, it may have difficulties to handle the cooling requirements. You can most likely expect coking problem in its coolant channels, which will lead to catastrophic engine failure if it indeed happens, as wel <div class="Discussion_UserSignature"> </div>

 

[propforce]

In case you're wondering the change of Isp with chamber pressure, Pc, here are the numbers.<br /><br />Pc (psia), O/F, Ivac (sec)<br /><br />150, 2.4, 361.2<br />500, 2.4, 364.4<br />1,000, 2.5, 366.1<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[drwayne]

Isn't soot in the chamber actually a good thing, in moderation?<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[gunsandrockets]

Great! Thanx for the info!<br /><br /><br /><Another thing, most liquid rocket engines use its fuel to cool its combustion chamber and nozzle. Since benzene has a very narrow liquid phase temperature range, it may have difficulties to handle the cooling requirements. You can most likely expect coking problem in its coolant channels, which will lead to catastrophic engine failure if it indeed happens, as well as serious soot formations in its combustion chamber. /><br /><br />Doesn't Benzene also burn at a higher temperature too, exacerbating those cooling problems?<br /><br />As you probably know, Benzene has been suggested as a propellant useful to a Mars Direct type manned mission and a Mars Sample Return type unmanned mission. The attraction is the lower percentance of hydrogen needed to manufacture a complete load of propellant on Mars, therefore reducing the mass of seed hydrogen that has to be brought from Earth. But as your information demonstrates there are a lot more factors involved that make for a good rocket propellant.<br /><br />Now if I can only coax you to respond to this post ... you could expand upon the virtues of propane.<br /><br />Your input to that thread was sorely missed!<br /><br />

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Isn't soot in the chamber actually a good thing, in moderation? <p><hr /></p></p></blockquote><br /><br />Yes, at low Pc (<1,500 psia) <i>some</i> carbon deposit on combustor walls actually reduces heat transfer so that's a good thing. At higher Pc (> 1,500 psia) the carbon will not deposit on combustor wall.<br /><br />The problem is in the "gut" of engine system, i.e., the gas generator (a fuel-rich combustor) and turbines where this "soot" (severe black smoke) is going to cover every gaps and surfaces with carbon deposits. Not sure how this will play out for a "re-usable" engine in Mars exploration.<br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Doesn't Benzene also burn at a higher temperature too, exacerbating those cooling problems? <p><hr /></p></p></blockquote><br /><br />Yes, benzene has more carbon atoms per molecule compare to RP-1 so it will burn hotter in the chamber. Combustion temperature for above cases are<br /><br />With LO2/ Benzene, Tc = 3839.8 deg. K<br />With LO2/ RP-1, Tc = 3546.7 deg. K<br /><br />So it burns roughly 300 deg. K hotter than RP-1. The cooling problem is already exacerbated mainly due to the thermal instability of benzene as coolant (from gumming & coking), but yes; the higher combustion temperature doesn't help. Another thing to consider, because of higher carbon atoms in the benzene therefore in the combustion gases, the radiation heat transfer contribution to the overall heat transfer to combustor wall will increase --- hence further exacerbating the cooling problem.<br /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Now if I can only coax you to respond to this post ... you could expand upon the virtues of propane. <br /><br />Your input to that thread was sorely missed! <p><hr /></p></p></blockquote><br /><br />I apologize for not participating ! That was a long thread with lots of good info. I will take the time to read them and contribute. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

<Yes, benzene has more carbon atoms per molecule compare to RP-1 so it will burn hotter in the chamber.><br /><br />I suspected as much. Thanx for the data.<br /><br />I was thinking, could you bypass the cooling problems of a benzene engine by cooling the engine with LOX instead?<br /><br />And since the engine normally runs extra hot, could you improve the ISP by running a higher mixture ratio with excess oxygen? I figure it might boost the ISP the same way a hydrogen engine boosts it's ISP by running fuel rich.