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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>All very interesting.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>A couple of comments:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div><div><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>></span></b>For a particular fuel under a particular operating condition, the size of the injector (a.k.a. "tiny hole") determines the level of air entrainment,<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I was not referring to this (though it is true for a pre-mixer). I was referring to the small hole that limits the propane flow into the (not premixing) propane burner head such as one finds with the ‘screw on’ top.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Like this:<o:p></o:p></span></p><p class=MsoNormal><img width=189 height=140 id="Picture_x0020_3" src="cid:image002.jpg@01D14A4F.BB6734F0"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>There is a jet inside that limits the flow, and there is no pre-mixed air, just a lot of tiny flames. When extinguished it doesn’t *pop*.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I have a BBQ that runs on propane and it has multiple flamelets on long tubes. I don’t think there is a pre-mixer in there. I looked…. When converting that same unit to natural gas there are pre-mixers on each line. That is a basic difference.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>My gas stove has a lot of pre-mixing but I doubt it is ‘full’. It is definitely using around the burner as well. But this one (American) looks like it has a pre-mixer at the bottom:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><img width=227 height=284 id="Picture_x0020_1" src="cid:image007.jpg@01D14A4F.BB6734F0"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>This one definitely does – you can see the adjuster:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><img width=551 height=258 id="Picture_x0020_2" src="cid:image003.png@01D14A47.7F012550"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>It is not true that "propane should generally not be premixed but natural gas should be". It will depend on the situation and application.<span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I can’t quibble. I am just reporting what I see and some reasons why. If a natural gas flame is not pre-mixed it needs more time and space to burn well. For a given number of Joules it needs more volume. This can be demonstrated (be careful!) by closing the premixing hole in a gas stove burner and watching what happens. To meet the USA requirement of 0.8% CO/CO<sub>2</sub> ratio the flame has to be completed just before getting to the pot. If the pre-mixing air is inadequate, it can’t do it. The flames are too long.<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>></span>Any flame operates equally well in any combustion mode. <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>That I have not experienced. It would be interesting to see. The combustion in my furnace (which is a pre-mixed natural gas flame x 4) is <i>terrible</i> if I close the air pre-mix holes. In fact there is a detector in place to shut it off if that happens. Is there a common device burning natural gas that does not use a premixed flame? <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Maybe this one is not pre-mixed:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><a href="http://www.cuisinartbbqs.com/en/ceramic_heat_technology.php">http://www.cuisinartbbqs.com/en/ceramic_heat_technology.php</a><o:p></o:p></span></p><p class=MsoNormal><b><span style='font-size:9.0pt;font-family:"Arial",sans-serif'>Propane Model #</span></b><span style='font-size:9.0pt;font-family:"Arial",sans-serif'> G35801 / 85-3112<br><b>Natural Gas Model #</b> G35802 / 85-3113<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Photo of it running (is the flame colour Photo-shopped?)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><a href="http://www.cuisinartbbqs.com/en/ceramic_smallspaces_photos.html#images/g35801-2_pic07.jpg">http://www.cuisinartbbqs.com/en/ceramic_smallspaces_photos.html#images/g35801-2_pic07.jpg</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>A 300 kW natural gas burner without pre-mixing is modelled <a href="http://www.academia.edu/3648228/Simulation_of_Non-Premixed_Natural_Gas_Flame">here</a> and please note that the gas comes through 24 ports and has carefully placed air directors to get the fuel mixed with it. Huh. There is a pretty big advantage to mixing first on a small scale, it seems.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>For the numbers, if I am not too far off, a kg of natural gas will contain about 309 moles of C,H and N, consume 124 moles of O2 and produce 14.65 m<sup>3</sup> of combustion products with no excess air at all (CO<sub>2MAX</sub> of 10.6%).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>A kg of Propane (99%) needs 113 moles of O2, creates 13.14 m<sup>3</sup> of products and has a CO<sub>2MAX</sub> of 12.6%. Not so different, is it?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Propane is easier to light 470 v.s. 580 and it doesn’t need as much air mixed in it to ignite: 2.1% v.s. 5%. Maybe the reason for natural gas to be (frequently) pre-mixed is just to make it easier to light with a ceramic sparker.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p></div></div></div></body></html>