cold oil raises or lowers fire rate?

mike morasco

If some one out there can help me with this counter-intuitive question. Cold oil raises or lowers your fire rate? Define fire rate? Is it just the sizing for a nozzel? If so cold fuel causes the nozzel to act as a "higher rate" nozzel.Is fire rate more tied to the over-all performance of a burner? In wich case colder oil less energy,poor atomization,less suface area for complete vaporization,fuel cooling down as travels away from optimum combustion zone. Thank-you for any help on this one.

Maine Ken

Oil flow rate can increase at low temps.

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Ken_40

Maine Ken's correct.

Your assumption regarding the nozzle is mis-placed.

The colder oil is more viscous. As a result, the positive displacement fuel-PUMP becomes slightly more efficient, allowing less oil to "leak" past the gear-set, and producing more flow. True, the regulator spring should keep the flow rate accurate, but it also has to deal with the more viscous oil and it too fails to pull back adequately.

The nozzle itself has little (to nothing at all) to do with the flow/firing rate.

This is why outdoor tanks above ground, oil not cut with winter additives and mobile homes use K-1, not # 2. It is a mis-guided attempt to keep the fuel viscosity from "gelling."

Dick Charland

I respectfully disagree with reason

Ken, the nozzle has everything to do with flow rate. It meters the quantity of fuel therefore the gph rating attributed to each one. The problem with cold oil is that the droplet size increases as it goes through nozzle due to viscosity. The fuel pump controls pressure through the regulator. One way to deal with cold oil is to raise pump pressure and decrease the flow rate (nozzle size) and generally the problem is solved. Discontinuing the use of a two pipe system also can help as we are not constantly bringing cold oil to the pump, substitute a Tiger Loop if necessary. Lastly, a nozzle line heater is another alternative solution.

realolman

very interesting nozzle article

Real interesting reading

In which the guy says the flow increases with viscosity... I suppose up to a point.

Anyone who messes with oil burners will find this article interesting Tells you everything you ever wanted to know about oil nozzles....I think you'll be saving a copy.

Ken_40

But...

A nozzel, say 1.00 GPH rated (of course we all know that is the rating at 100# and 100# ONLY!) wll go from the pump, thru the "jet tube" into the 1/8" diameter pipe/transport pipe, into the adapter nut, then thru the nozle filter (and cavity it is threaded to and ultimate thur the slot array, then be ejected from the tip orifice.

A firing rate of 1-gallon per hour will result in whatever the temp of the oil was, while in the fuel unit (pump) being expose through extremely themally conductive (copper and brass) environs INSIDE THE BURNER, AND AT THE END - IN DIRECT RADIANT INTIMACY OF THE FLAME'S RADIANT ENERGY.

At 1-GPM, only 2 oz of fuel will pass thru the tubing from fuel unit to nozzle orifice in an entire second. Given the volume the steel tubes, copper and brass adapter, nozzle and jet tube contain, the oil is warmed significantlt from end to end of its internal route. Not only must the oil pass thru the warmed area described, it is in the presence of the fan's air path, providing even more effective warming of the oil pathway by the basement air the fan will inject accross the tubing. This air would minimally be 60 degrees. Given the proximity to a warm iron boiler mounting plate and the boiler itself, 70-80 degree air would be even more probable.

In short, the oil coming thru the nozzle is much warmer than the oil passing thru the fuel unit/pump. A LOT warmer.

Agreed: A one pipe setup would make it even warmer.

RonWHC

Cold oil has

higher viscosity than warmer product. High viscosity leads to larger droplets thru the nozzle. Larger droplets equal more oil. The larger droplets also result in poor ignition, flame noise, smoke, & the signature fire burning off the chamber target wall.

The quickest solution is smaller nozzle & higher fuel unit pressure. Consult your pressure chart. The higher pressure results in improved atomization (smaller droplets). But, please, please, tag the burner that the fuel unit pressure has been increased. Otherwise, some oily burner tech may put the prior nozzle size back in @ the increased pressure.

Ken_40

Large droplets mean

large droplets. Period.

Small droplets means small droplets. Period.

Flame and combustion properties are the result of many factors, one of many - is size of the droplet. The droplet size does not determine the firing "rate." The droplet size DOES determine the nature of the flame and MAY impact firing rate, but is NOT directly responsible for the amount of oil fired, merely the aftermath of a bunch of other factors.

Weezbo

i have a copy of that*~/:)

excellent read.

when i get home from work today i will try to find another excellentpdf to add to your arsenal *~/:)

[Deleted User]

\"as the viscosity of the fuel

flowing through the nozzle increases, so does the flow rate. As higher viscosity oil passes into the nozzle through the tangential slots and into the swirl chamber, the rotational velocity is slowed down. As a result, the walls of the tube of oil leaving the orifice are thicker, hence more oil enters the chamber and the droplets are bigger".

NORA Oilheat Technicians Manual 2002 Edition Chapter 4 Page 85.

Ken_40

I have no doubt

the state ment is correct, but very marginally; and to the point of being so marginal - as to be virtually inconsequential.

To wing a number, I would suggest the viscosity change has an impact of 10:1. The 10 being the gearset issue. The 1 being the nozzle.

But I must recant the notion that ONLY the fuel unit makes a difference in the firing rate. Yet I have lingering doubts about the issue of semantics. Principally, the quality of the flame vs. the actual number of GPH being consumed.

Thanks for the "heads up" Ron.

chapchap70_2

The spray angle also decreases with the larger droplet size according to the Oil Heat Technicians Manual that I have. I don't think the people who write the books put stuff like that in it if it was only about inconsequential semantics.

Do you still think that the people who thin the oil with kero or use additives are misguided?

Aaron_2

When was the last time you could specify

the gearset of a fuel unit?? Obviously that would make a difference in a world where the gearset could be changed depending on the fuel conditions, but here in the real world, we all work with the same gear sets, and therefore can only change the pressure and the nozzle to attempt to accomidate the fuel conditions, which usually means with cold oil, raise the pump pressure, lower nozzle fire rate and possibly lessen the angle of spray to help with the droplet size.

Lurkin' Murkin'

Pump changes?

If the amount of oil going through the nozzle is only a fraction of what the pump is able to push, how is the viscosity at the gearset relavant? Isn't the pressure to the nozzle line the same, regardless of oil temperature?