Thanks for the comments. I sense there is still some confusion, maybe it helps to use figures from the experiment of Roefisher. He is boiling 600 ml water, let's say he uses 10 g of fuel. That is around 12 ml of kerosene or 13 ml petrol. When that fuel is heated to 300 degrees it expands to a gas, it will be around 1 L of kerosene gas or maybe 1.4 L of petrol gas. Don't take these numbers literally, I haven't calculated exactly, it could be 0.7 vs 1.0 L or even 1.5 vs 2 L. Anyway, it takes 3 min 30 s for the 1 L of kerosene gas to pass the jet, but almost 5 min for the 1.4 L petrol gas to pass that same jet. Same amount of fuel in grams, slightly more petrol in ml liquid. Same amount of energy in total. The end result is that the stove produces less power (as in: energy per time unit) when burning petrol than with kerosene. If you don't change the jet. Yes there will be many other factors, but this is the main explanation. It also explains why the OP notices soot when burning kerosene. I don't think I will buy a stove sold with the argument that one jet fits all fuel. I don't see the point - and the experiment of Roefisher also shows why it's a bad idea, you will always either be low on power or get soot. How often do you change fuel on the fly? Unplanned? Without being able to hold off the wolves the ten minutes it takes to change the jet.
@OMC @z1ulike @Ed Winskill Part of the confusion/disagreement in comparing gasoline to kerosene is that when one states a value for the energy it is important to note what are the units in the denominator. Comparing energy per gram (where kerosene and gasoline pretty much the same) is going to be different than energy per ml (kerosene is denser, so more energy). The 30%-40% value Radfahrer gave is per molecule. White gas is mostly heptane (7 Carbons), if the average length of kerosene hydrocarbons is 10 carbons, then a molecule of gasoline is 7/10 the mass of kerosene and the heat generated by combustion will also be less by about the same ratio.
@itchy another thing to remember is that both gasoline and kerosene are mixtures of many compounds which vary from batch to batch and over time. So any measure of energy will be an approximation no matter how well designed the test. This being a stove site, comparing fuels by volume or weight is useful and approximates real world results. Since switching from gasoline to kerosene will not boil water 30%-40% faster your molecular comparison is misleading. "If your experiment needs statistics, you ought to have done a better experiment." Ernest Rutherford Ben
I sometimes measure the output of a burner by weighing the stove on a kitchen scale before and after a 5 minute burn. I then multiply the mass of the burned fuel by its lower heating value and divide the result by 300 (300 seconds = 5 minutes). That gives me the power output in watts (or btu if that your thing). I'll bet you that the output of a kerosene burner on gasoline is way less than a kerosene burner on kerosene. On modern multifuel stoves you have to install a larger diameter jet, when you go from kero to gas in order to increase the fuel flow rate.
Well, according to the OP that is exactly what happens. And, Radfahrer does a good job explaining why that might be the case. Nothing misleading at all. No statistics necessary.
Or (as in the case with the Optimus Polaris Optifuel) accept the differences in output when using different variants of fuel - since there are only that "one jet for everything" option provided by the manufacturer... I've found my Polaris is by far best on a kerosene type fuel, but it operates OK on just about anything liquid (except alcohol!) or gaseous over the entire span between diesel and gas (propane, butane or mixes...) Haven't tried it on methane. Yet... Works good enough for me! - so I'll be replacing my KAP Arctic with a 25 ULHA windscreen set + a Polaris in Trangias adapter cup, with DuoSSAL pots and pan. And stubbornly keep using kerosene (got a barrel of Jet-A1 to use up so I'll be good for eternity. Well almost)... For remembering all the good times we've had together: I'll probably put the KAP in the living room display cabinet. :-) /Odd
Almost century they have used different size of jet for different fuels. There has been a reason for that and modern stove manufacturers have not been able to change that reason. Origin for reason must be in physics of fuel flow, mixing of fuel vapor to the air and burning of the mixture. So "one jet for all fuels" stoves are a bit compromise for some of fuels that it uses. Many stovies have found easy solution for that fuel challenge: They have several stoves for different fuels. Multifuel stoves are used with some fuel and jets for other fuels are carried with stove for situations where you need to use another fuel. @Odd If you living room cabinet is not able to accommodate that retiring KAP I would be interested to buy it.
