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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>There is quite a good pic of flames at various mixed levels in <a href="https://en.wikipedia.org/wiki/Bunsen_burner">https://en.wikipedia.org/wiki/Bunsen_burner</a>. When there is no premixing, the flame is yellow and dirty (not all carbon is combusted, as in a candle flame). When you get to a stoichiometric flame, all the combustion takes place at the blue cone – the almost invisible “flame” above it is mainly hot gas radiating; minimal combustion takes place there.<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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Prof Philip Lloyd</span><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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Energy Institute</span><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:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cape Peninsula University of Technology</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PO Box 1906<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Bellville 7535<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Tel: 021 959 4323<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Fax: 086 778 0257<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Cell: 083 441 5247<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-ZA style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>PA: Nadia 021 959 4330<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='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Stoves [mailto:stoves-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>Crispin Pemberton-Pigott<br><b>Sent:</b> 09 January 2016 03:04<br><b>To:</b> 'Discussion of biomass cooking stoves'<br><b>Subject:</b> Re: [Stoves] venturi system -ratios of air and gas?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>All very interesting.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA 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 style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>></span></b><span lang=EN-CA>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></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Like this:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA><img border=0 width=189 height=140 id="Picture_x0020_3" src="cid:image001.jpg@01D14ABA.4F0141F0"></span><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA><img border=0 width=227 height=284 id="Picture_x0020_1" src="cid:image002.jpg@01D14ABA.4F0141F0"></span><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA><img border=0 width=551 height=258 id="Picture_x0020_2" src="cid:image003.png@01D14ABA.4F0141F0"></span><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='color:#1F497D'>></span><span lang=EN-CA>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></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='color:#1F497D'><o:p> </o:p></span></p></div><div><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>></span><span lang=EN-CA>Any flame operates equally well in any combustion mode. <span style='color:#1F497D'><o:p></o:p></span></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA 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 lang=EN-CA style='font-size:9.0pt;font-family:"Arial","sans-serif"'>Propane Model #</span></b><span lang=EN-CA 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 lang=EN-CA 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 lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Propane is easier to light 470œ v.s. 580œ 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 lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p></div></div></div><div style="position:absolute;margin:15px 0 0 0px; padding-top:10px;padding-right:15px;min-width:350px; border-top:1px solid #ccc;font-size:12px; color: #333; font-family:arial,'Hiragino Sans GB',Tahoma,Helvetica,STHeiti; ">This email has been protected by YAC (Yet Another Cleaner) <a href="http://www.yac.mx?source=email" style="display:block;padding-top:5px; color:#2bafed;text-decoration:none;">www.yac.mx</a></div></body></html>