Difference between revisions of "Fuel meter"

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A '''fuel meter''', also known as a '''propane meter''' is used to inject a predetermined amout of fuel gas (usually [[propane]]) into the chamber of a [[Combustion cannon|combustion]] or [[hybrid cannon|hybrid]]. It typically consists of an adjustable [[pressure regulator]] and [[pressure gauge]], connected to two [[ball valve]]s with a length of pipe in between. The volume of this pipe and the pressure of the gas determines the amount of gas injected. The second ball valve is connected to the chamber of the gun.
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A '''fuel meter''', also known as a '''propane meter''' is used to inject a predetermined amount of fuel gas (usually [[propane]]) into the chamber of a [[Combustion cannon|combustion]] or [[hybrid cannon|hybrid]]. It typically consists of an adjustable [[pressure regulator]] and [[pressure gauge]], connected to two [[ball valve]]s with a length of pipe in between. The volume of this pipe and the pressure of the gas determines the amount of gas injected. The second ball valve is connected to the chamber of the gun.
 
A fuel meter is operated as follows:
 
A fuel meter is operated as follows:
 
*The regulator is set to a predetermined pressure for the particular meter and chamber size
 
*The regulator is set to a predetermined pressure for the particular meter and chamber size

Revision as of 05:47, 3 June 2007

A fuel meter, also known as a propane meter is used to inject a predetermined amount of fuel gas (usually propane) into the chamber of a combustion or hybrid. It typically consists of an adjustable pressure regulator and pressure gauge, connected to two ball valves with a length of pipe in between. The volume of this pipe and the pressure of the gas determines the amount of gas injected. The second ball valve is connected to the chamber of the gun. A fuel meter is operated as follows:

  • The regulator is set to a predetermined pressure for the particular meter and chamber size
  • The ball valve closest to the regulator is opened, filling the pipe up until the second ball valve with gas at the regulated pressure
  • The first ball valve is closed again, closing off the section of pipe between the two valves
  • The second ball valve is opened, the pressurized gas inside the meter expands and enters the main chamber
  • The second ball valve is closed, and the cannon is ready to fire

The regulator usually only needs to be set the first time, and further fueling can be done simply by opening and closing the two ball valves. A fuel meter provides fast and very consistent fueling, and is the easiest way to use bottled gas for fuel.

Calculations

Constructing a fuel meter and determining the correct pressure to use requires a few calculations. First you need to calculate the fuel:air ratio, and from that the amount of fuel needed. These calculations are covered under stoichiometry.


Formulas for fuel meters:

P=pressure in bar, Vf=fuel volume, Vm=meter volume. Any unit of measurement can be used for the volume, as long as the same unit is used throughout. Pressure needs to be converted to bar, if you have the pressure in psi divide it by 14.7.

  • P = Vf/Vm
  • Vm = Vf/P
  • Vf = P*Vm

Concrete example

In the example from the stoichiometry article, we found that the fuel volume needed for a 3000 cc chamber is 126 cc. At 1 atmosphere (14.7 psi) of overpressure, we'd need a meter volume of 126 cc. At twice the pressure, we'd need half the volume and so on.

For the example, we decide that meter pressure will be 3 bar. The meter volume required is then 126/3 = 42 cc.


The Fuel Tool (found on Burnt Latke's performance calculators page) automates the fuel meter calculations.