A proper ratio of gaseous (vaporized) fuel to air is required for combustion. Every fuel has a flammability range. Combustion is only possible if the fuel-air ratio is within the flammability range for the fuel. A fuel’s flammability range refers to the percentage of the fuel, in its gaseous state, to air to create a combustible or explosive mixture. This varies with different flammable liquids. Gasoline has a flammability range of 1.4 % to 7.6 %. This means gasoline will ignite when there is 1.4 parts of gasoline mixed with 100 parts air. Thus, 1.4 % is known as the lower flammable limit and 7.6 % is the upper flammable limit of the flammable range. A product mixed with air below the low end of its flammable range is too lean to burn. A flammable liquid that exceeds its upper flammable limit is too rich to ignite. Ethylene oxide is extremely flammable. It has a flammable range of 3.6 % to 100 %. This means it can burn even if there is no air.

Gasoline has a narrow flammability range. A car’s carburetor must precisely meter the fuel-air mixture to obtain the desired flammable range. A vehicle will have trouble operating if the carburetor meters too much gasoline (called a rich mixture) that is generally distinguished by a black exhaust from the car and the smell of unburned hydrocarbons. Too little gasoline in a vehicle's carburetor is called a lean mixture, which is too diluted for ignition. The same is true for kerosene (or gasoline for the earlier Stanleys) and its mixing and combustion in the Stanley burner.

The design of a Stanley burner is that of a shallow can. At the top of the can is the burner grate that contains holes or slots. As the fuel burns on top of the grate it draws in air and fuel from beneath the grate. This causes a partial vacuum within the interior of the burner "can". A pair of 1-1/2" diameter mixing tubes are inserted into the sidewalls of the "can" under the grate. The mixing tubes draw in air to make up for the air being drawn from the interior of the "can" to the topside of the grate where burning is occurring. As the air is drawn into the mixing tubes gaseous fuel under pressure is also injected at the proper fuel-air ratio into the center of the mixing tubes. As the gaseous fuel and air travel the length of the mixing tubes a through mixing occurs. As the mixture exits the tubes it is drawn through the slots of the burner where it is burned above the grate.  Pictured at the left is a Cruban burner mounted to the underside of a 20-horsepower Stanley boiler.

The other ingredient of the combustion process that the burner provides is a continuous ignition source above the ignition temperature of the fuel-air mixture. The ignition temperature is the temperature required for a liquid to continue to emit flammable vapors that will sustain combustion. Gasoline will ignite when a heat source or electrical spark of at least 853 degrees comes in contact with it. Natural gas (methane) needs an ignition temperature of around 1000 degrees and paint thinner 453 degrees. For the Stanley burner the flame of the pilot provides an ignition temperature will above the minimum required for the air-fuel mixture.

One other aspect of a fuel of importance is its vapor density. The vapor density of a fuel is the weight of a vapor relative to the weight of air. The vapor density of natural gas causes it to be lighter than air and thus natural gas will rise when exposed in the open. The vapor density of gasoline and kerosene is heavier than air and will seek low points when it is exposed to the air. Products with a high vapor density (heavier than air) behave much like carbon dioxide gas escaping from a block of dry ice (dry ice is frozen carbon dioxide gas) where the vapors leaving the dry ice flow across the surface the dry ice is resting on.

Where remembering the vapor density of gasoline and kerosene is important is that the design of the Stanley burner provides ample space within the burner for the fuel vapors to accumulate. This accumulation is hazardous if an ignition source is available. Thus it is always important to remember the potential for vapors to "pop" around a Stanley burner. Caution must always be exercised when working around a Stanley burner. 

There are many types of burners used on Stanley steam cars. While cars were shipped from the factory with a Stanley burner installed, many owners over the years changed to an aftermarket burner. Such names as Cruban, Baker, and Ottaway are some of the more common ones in use.

Stanley grates are cast iron and are heavy and thick. Built two types, slotted and drilled, the burners were always the same diameter as the boiler. Stanley burner grates have flat peaks milled flat for about 1" of width. Between each of these flat peaks were valleys about 1" wide and 1" deep. These valleys were leveled to the height of the peaks with insulation to keep the heat off of the grate. The slotted grate had short slots milled across the top of each ridge. The drilled burner grate has thousands of holes drilled through the ridge to allow the air/fuel mixture to pass. The slotted grate was used up to about 1914. After1914 the drilled grate was used with either of their two fuel systems.

The Baker burner utilizes a thin, slotted, flat grate casting. The long slots allow much more air/fuel mixture through than the other types of burners. They are known to give the most heat of any burner. Baker’s mixing tubes were nearly twice the cross-sectional area of a pair of Stanley nozzles.

The Ottaway style burner is a fabricated burner that is easy for hobbyists to build. It is a round pancaked air chamber with fuel mixing tube in the front like the others. The chambers top grate area is 5/32 " thick # 321 stainless plate. The bottom plate is identical but without the holes obviously. The grate area is solid (no insulation) with #54 drill bit holes laid out on a grid.

Cruban offered a burner and pilot light combination of their own design. Their burners were much heavier than a Stanley being all cast construction. Cruban also built Stanley burner bottoms using their Nichrome heat resisting lining. A Cruban grate is similar in design to the Stanley slotted design. Cruban’s aftermarket pilot for use with a Stanley burner looked different in that they had a vertical air intake.  Click on the following link to view a series of advertising cards describing the design features of the Cruban burner.  Also see the Steam Automatic article for information relating to the Cruban Steam Automatic.

~ Cruban Empire Burner Advertising Cards ~

Pictured to the left is a Cruban burner belonging to Bruce Magnell undergoing a test firing.  This burner has been rebuilt and is being tested prior to being put under a boiler.  During testing a specific amount of kerosene was put in a tank and the tank pressurized to a given pressure.  The burner was lit and allowed to consume all the fuel.  The fuel consumption rate of the burner was then determined.