Trivia(l) Question for Rocket Scientists...

[darkenfast]

I was just wondering; the Shuttles SSME's (LOX/LH) produce a clear exhaust, sometimes with shock diamonds visible. The Delta IV's engine, burning the same oxidizer/fuel, has a yellow-orange color to its exhaust. Is it because of cooler burning? Less efficiency? Expiring minds want to know! Thanks in advance.

 

[rfoshaug]

I was wondering the same thing. I was rather surprised by the long orange flames of the Delta IV Heavy.<br /><br />I believe the Delta IV engines are much more powerful than the SSME's (twice the power?)... Maybe it's easier to achieve perfect burning in a smaller engine?<br /><br />If anyone knows why the Delta IV has such long flames, I'd be very happy to know. <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>

 

[vogon13]

SSME exhaust is 6000 degrees F. Radiates a great deal of UV light, which you don't see.<br /><br />With the fuel being H and the oxidizer O, you could consider the SSME to be the ultimate steam engine. Simon and Fulton would flip!<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[tomnackid]

Just as an aside, my favorite "proof" that we didn't really land on the moon is that the exhaust of the LEM taking off from the surface of the moon was not as visible as it was in the artist's representations!<br /><br />Of course ask these conspiracy theorists what hypergolic propellent being burned in full unfiltered sunlight, photogrpahed by a circa 1960s color video camera and transmitted 1/4 of a million miles to a circa 1960s TV screeen is SUPPOSED to look like and they haven't got a clue. <br /><br />So in other words, "It doesn't look like what its supposed to look like even though we haven't got a clue what that is in the first place."!

 

[bpcooper]

The blue triangles are called 'blue mach diamonds' and are an indication of smooth, supersonic flow coming out of the engines.<br /><br />I was not aware that they are "colored" so to speak.<br /><br />And yes, the Delta 4 engines are 650,000 lbs thrust a piece at full throttle while the Shuttle is 375,000 (both sea level). Almost double. <div class="Discussion_UserSignature"> <p>-Ben</p> </div>

 

[bpcooper]

Oh, I see now. Thanks. <br /><br />I think another reason we see the orange flame is because there are no SRBs to drown it out. On Delta 4 medium with SRBs you cannot see the main engine's flame. Same with the Shuttle. If you look carefully in some photos you can indeed see the stream coming out (yellow/orange flame) a long ways as seen in my first shot here:<br /><br />http://www.launchphotography.com/STS-114.html<br /><br />I think if the Shuttle could be launched with no SRBs, it would appear just like D4. <div class="Discussion_UserSignature"> <p>-Ben</p> </div>

 

[trailrider]

I don't know the details of either SSME's or the Delta IV core engine designs. It may be that a different injection/combustor design, plus differences in the operating pressures have something to do with it. I believe I recall the SSME's operate at about 2,975 psia, which when they were designed was quite high. Don't know about the Delta IV engines. A lower P-sub-c might make quite a difference.<br /><br />Also, I don't know the expansion ratios of the nozzles on both birds. It may be that the Shuttle engines are optimized for a different altitude as they burn through the entire launch sequence, whereas the Delta IV has upper stages that are optimized for higher altitudes.<br /><br />Also, as someone else pointed out, the opaque exhaust of the solid rocket boosters drowns out the relatively clear exhaust of the SSME's, as is also the case when the Delta IV has SRM's on the sides.<br /><br />Hypergolics have a different colored exhaust, depending on the propellants. In the vacuum of space there is also no reaction with atmosphere.<br /><br />Ad Luna! Ad Aries! Ad Astra!<br />Trailrider

 

[propforce]

<i>".... Somebody with inside knowledge said that it was positively that Delta 4 has an ablative nozzle. Material from the nozzle 'burns' off by design and colors the flame. ..."</i><br /><br />That would be the Shuttle_Guy <img src="/images/icons/wink.gif" />, who is correct in that the ablative nozzle added the carbon particles which radiates more brightly than hydrogen and added colors to the exhaust flames. <br /><br />A kerosene engine shows the similar yellowish flame because of the carbon particles in the exhaust. <br /><br /><br /><br /><i>"..... That first launch also had us close to cardiac arrest when the insulation just above the engine caught fire. We didn't know that was semi-expected too...."</i><br /><br />So much for a paint job !! <img src="/images/icons/laugh.gif" /> This was compounded by the fact that DIV has an enclosed exhaust pad and that the RS-68 is a 'fuel-lead' during engine start, dumping gaseous hydrogen that had nowhere to go but UP. The leftover hydrogen got spontaneous ignited when engine starts, adding a perfect flame source to burn all those insulations. <br /><br />The management did not want to spend the money putting in a water spray system in the exhaust duct. After the DIV-Heavy launch, they've found several structural steel as well as concrete were burned and eroded away and had to do some major repairs. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<i>".... I think if the Shuttle could be launched with no SRBs, it would appear just like D4. ..."</i><br /><br />I was fortunate to have witness a SSME firing at MSFC test stand, where they place a water-cooled camera under the engine during firing. The exhaust flame of a SSME is so clear such that you can see the all the way to the injector head. <div class="Discussion_UserSignature"> </div>