Pics and info submitted by ECN Member Alan Belson.

Here's how I solved the unburned-oil and jet clogging I met with in my earlier machines,HERE, to make a reliable and efficient Vegetable Oil central heating burner. I’ve accepted the compromise of blending VO with diesel oil, though the fuel is no longer entirely 'free'. Features of this burner, built from a recycled pressure-jet unit, are- A dual-fuel system, rationalised electrical fuel-heating, a new exhaust gas re-circulating combustion chamber and additional electrical controls, the latter forming most of the modifications.

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Schematic burner assembly. Burner ignites with residual neat diesel oil. Simultaneously, a VO/diesel oil blend is being made at the burner gear-pump. This fuel blend takes about 20 seconds to reach the nozzle, [depending on line volume and fuel consumption]. When the 'programmer call' ceases, [or the boiler thermostat is satisfied], the VO supply pump switches off. Diesel oil then flushes VO from the burner, because a delay timer prolongs the burn by 30 seconds. This only raises the boiler temperature by a few degrees C above normal. Residual neat diesel oil is thus present for the next start. With the combustion chamber fitted it solves the VO polymer clogging problem, giving assured ignition and superb combustion.


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Finally, a fan-only sequence cools the 3 lb + weight combustion chamber to protect upstream components from inertial heat, by using a 50 second delay timer. This pic, taken at burn termination, shows why!


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Detail drawing of the combustion chamber. 316 grade stainless steel was used for its high temperature qualities.


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Combustion chamber, new gasket, spilt sleeve and fittings. The additional drillings are from trials experimental dead-ends. The combustion chamber is designed to re-circulate a percentage of hot exhaust-gas to improve combustion by the gasification of fuel. The band clamping method, [ex dairy supply house], proved very strong and rigid.


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Burner on bench trials at c. 21kW. Two motors are fitted, [separating the air-fan and gear-pump functions], to let me use an existing Danfoss LE pump which unfortunately counter-rotated to the original motor & fan on my donor burner. It auto-depressurises the Protek nozzle valve [see later] on idle. A dummy firebox is used in trials to mimic furnace conditions. Recirculation of exhaust only occurs when combustion is so confined. The flame colour is an ephemeral pink, probably due to alloy traces from the firebox’s stainless steel sheet. Otherwise, the flame is clear, with no unburned fuel, smoke, smell of fries or visible soot from the start to finish of the burn. I settled on running c. 50% VO / 50% D during trials, a very sensible and conservative blend for this machine. I aim to increase the VO ratio in long-term trials on the boiler using a gas analyser and a few slight modifications. Nozzle fitted : Delavan 0.5 GPH 80º hollow cone, oil pressure 150psi with a 135psi Protek anti-dribble valve, depressurised on idle by the Danfoss LE pump.


[Linked Image from electrical-photos.com]