An air-and-gasoline torch mixes vaporized liquid fuel with air to produce a directed flame. The illustrated pressure-blowlamp arrangement uses a reservoir, hand pump, heated vaporizer and air-mixing burner. Explore the fuel-energy rate, an assumed combustion factor and nominal air demand; the calculator does not determine flame temperature, operating pressure or heating time for a workpiece.
Air and Gasoline Torch Interactive Calculator
Estimate fuel heat-release rate with an entered combustion factor, nominal stoichiometric air demand and heat rate per tip area. Workpiece heating and burner settings are not calculated.
Equation Used
The calculator multiplies fuel flow by lower heating value and an entered combustion factor, dividing by 3.6 to convert MJ/hr to kW. This is an estimated heat-release rate, not the heat absorbed by a workpiece. The two heat cards show the same quantity in different units.
- Gasoline vapor is fully vaporized before the mixing chamber.
- Lower heating value is used rather than higher heating value.
- Nominal stoichiometric air is estimated at a fixed 14.7 kg air per kg fuel. Actual fuel composition changes this ratio, and burner air settings require separate information.
- Tip loading is the calculated heat-release rate divided by circular tip area. It is not measured heat flux onto the work or a nozzle rating.
From liquid fuel to a directed flame
The hand pump pressurizes the illustrated reservoir. Fuel passes through a heated vaporizer, and the vapor jet mixes with air before combustion at the burner. Heat from operation helps sustain vaporization. Other liquid-fuel burner arrangements can use a separate air supply; they should not be assumed to share this diagram’s components or settings.
Main components
- Reservoir and pump: contain and supply the fuel in the pressure-blowlamp arrangement.
- Metering passage: controls the fuel delivery.
- Vaporizer: transfers heat to the fuel before mixing.
- Air inlet and mixing passage: bring air and vapor together.
- Burner outlet: directs the mixture and supports the flame.
Fuel composition, vaporization, mixture velocity and heat feedback affect operation. Flame color alone cannot establish a correct pressure, complete combustion or safe condition. The drawing does not specify a pressure rating, relief setting, seal material, fuel substitution, tip modification or lighting procedure.
Local heating and thermal calculations
Liquid-fuel torches illustrate how stored chemical energy can be delivered as a localized flame for heating and metalworking. Whether a particular unit is suitable for soldering or brazing depends on the manufacturer’s intended use, the material, the filler and the joint geometry.
The calculator is useful for comparing assumed fuel-energy rates and unit conversions. A given kilowatt result cannot guarantee a joint temperature, heating time, finish quality or process approval. Those also depend on flame-to-work heat transfer, losses, workpiece mass and thermal properties.
Heat-release rate and nominal air demand
For fuel flow m in kg/hr, lower heating value H in MJ/kg and dimensionless entered factor η, Q = mHη/3.6 in kW. The divisor converts MJ/hr to kJ/s. Multiplying kW by 3,412.142 gives BTU/hr.
If η represents combustion efficiency, it accounts for incomplete release of chemical energy. It does not automatically include heat-transfer losses to the surroundings or workpiece. An efficiency entered as a fraction must not be mistaken for a percentage; 0.90 represents 90%.
Nominal Air = 14.7m in kg/hr. The fixed ratio is a gasoline approximation, not an air-pressure setting. Actual stoichiometric demand varies with fuel composition; excess air and burner mixing also matter.
For entered tip diameter d in mm, the circular area is πd²/4. Tip Loading is Q divided by that area in kW/mm². Fuel flow is independently entered, so changing tip diameter does not change heat release in this model. It changes only this area-based indicator and the illustrated nozzle inset.
The calculator does not solve fuel pressure, discharge coefficient, exit velocity, flame stability, combustion temperature, emissions or heat absorbed by the work.
Worked example: energy rate and tip area
Take hypothetical inputs of fuel flow 0.30 kg/hr, lower heating value 44 MJ/kg, factor 0.90 and tip diameter 1.5 mm. These inputs are not operating instructions for a torch.
Heat release is 0.30 × 44 × 0.90 / 3.6 = 3.30 kW, or approximately 11,260 BTU/hr. Nominal air demand is 0.30 × 14.7 = 4.41 kg/hr.
Tip area is π × 1.5² / 4 ≈ 1.7671 mm², giving Tip Loading ≈ 1.8674 kW/mm². This is heat rate divided by outlet area, not the heat flux received by a joint.
At fuel flow 0.15 kg/hr, the same assumptions give 1.65 kW and 2.205 kg/hr nominal air. At 0.60 kg/hr they give 6.60 kW and 8.82 kg/hr. The calculations do not determine how to obtain those flows from pressure or valve position, and they do not predict a brazing time.
Comparing burner arrangements
| Arrangement | Fuel delivery | Distinguishing feature |
|---|---|---|
| Liquid-fuel vaporizing torch | Liquid supply followed by vaporization. | Vaporization and heat feedback are part of burner operation. |
| Fuel-gas and air torch | Fuel gas mixes with air. | Gas delivery and air entrainment depend on the particular burner. |
| Oxygen-fuel torch | Separate fuel and oxygen supplies. | Requires equipment designed for both gases and their specified delivery conditions. |
Rated output, compatible fuel, pressure, duty and intended process are equipment-specific. A generic mechanism comparison does not establish that one torch or fuel can substitute for another.
Torch calculation questions
No. The result estimates fuel energy released after the entered factor. Workpiece heat absorption requires a separate heat-transfer calculation or measurement.
Fuel mass flow is an independent input. Diameter changes circular outlet area and the Tip Loading indicator; the calculator does not derive flow from the nozzle or pressure.
No. It is the fixed nominal ratio used here. Stoichiometric air demand varies with chemical composition, including oxygenated components.
No. It does not solve operating pressure or flame stability. Use the instructions and rated equipment for the particular torch; appearance or a paper test is not a pressure measurement.
Not by assumption. Fuel compatibility is specific to the equipment. This generic diagram and energy calculation do not authorize fuel substitutions.
The calculator cannot diagnose that fault. Stop using a malfunctioning unit and follow its manufacturer’s shutdown and service instructions; changing a tip or improvising a screen is not a general remedy.
This calculator multiplies kW by 3,412.142. Thus 3.30 kW is approximately 11,260 BTU/hr. The conversion does not add a separate heating capability.
References and further reading
U.S. Department of Energy: Fuel Property Impacts and Limitations on Combustion includes measured fuel heating values and composition-dependent stoichiometric ratios. It concerns engine fuels, not torch operating instructions.
Bernzomatic product manuals illustrate the need for model-specific fuel and operating instructions for modern torches; those instructions are not specifications for a historical gasoline blowlamp.
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