SpudFiles Wiki - User contributions [en]

DDT

2007-10-23T08:18:49Z

Pete Zaria:

"DDT" stands for Deflagration to Detonation Transition and is the technical term for the little-understood phenomenon that occurs when the flame front inside a burning fuel/air mixture reaches and exceeds the (local) speed of sound. Note that the speed of sound changes with pressure, temperature, and even humidity, so the speed of sound inside the combustion chamber can be very different from the atmospheric speed of sound.

In a normal combustion situation, the flame front in a burning fuel/air mixture does not exceed the speed of sound, classifying it as a deflagration (see [http://en.wikipedia.org/wiki/Deflagration Deflagration on Wikipedia]). The combustion inside a gasoline or diesel engine, gunpowder, and low-grade explosives are all deflagrations.

Under rare circumstances (generally in respectively long, thin combustion chambers containing pressurized fuel/oxidizer mixtures), the flame front can exceed the (local) speed of sound, as does the flame front of high explosives, classifying it as a [http://en.wikipedia.org/wiki/Detonation Detonation]. This transition from subsonic to supersonic can create an immense pressure spike that has damaged even well-constructed metal chambers, and is certain to cause a PVC chamber to fail.

It is the goal of anyone who constructs a [[hybrid]] launcher to avoid DDT. It is thought that a short, fat (theoretically closer to spherical) chamber is less likely to incur DDT than a long, thin chamber. Using oxygen enriched mixtures or exotic fuels such as acetylene increase the risk of DDT.

For more information on DDT, try [http://www.google.com/search?hl=en&q=deflagration+detonation+transition&btnG=Search Google].

Hybrid cannon

2007-10-23T08:16:38Z

Pete Zaria:

[[Image:hybrid.jpg|right|thumb|300px| A very well constructed hybrid cannon]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher pressure and temperature gases generated by a hybrid combustion.

A hybrid launcher consists of seven basic elements:

*High pressure combustion chamber
*Pressure-triggered main valve (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually schrader or quick connect)
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, [[pressure gauge]]s and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], flyback, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is the most dangerous type of launcher that can be built. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]) such as Sch. 80 PVC, or even better, metal pipe and fittings. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must, and the limit of a 4x propane/ 4 atmosphere mix should never be breached when using any type of plastic pipe. If a higher mix is attempted, [[DDT]] (deflagration to detonation transition, where the flame front exceeds the sound barrier in the combustion gases) theoretically can occur, causing an extreme pressure spike. No plastic pipe can handle this pressure spike, and will probably shatter, launching plastic shards everywhere. A chamber made of steel, iron, or aluminum can survive higher mixes than 4x propane/ 4 atmospheres, and have been used at up to 8x propane/ 8 atmosphere mixtures. However, utmost care must be taken with these launchers, in construction and materials used.

DDT

2007-10-23T08:12:01Z

Pete Zaria: New page: "DDT" stands for Deflagration to Detonation Transition and is the technical term for the little-understood phenomenon occurs when the flame-front inside a burning fuel/air mixture reaches ...

"DDT" stands for Deflagration to Detonation Transition and is the technical term for the little-understood phenomenon occurs when the flame-front inside a burning fuel/air mixture reaches and exceeds the (local) speed of sound. Note that the speed of sound changes with pressure, temperature, and even humidity, so the speed of sound inside the combustion chamber can be very different from the atmospheric speed of sound.

In a normal combustion situation, the flame front in a burning fuel/air mixture does not exceed the speed of sound, classifying it as a deflagration (see [http://en.wikipedia.org/wiki/Deflagration Deflagration on Wikipedia]).

Under rare circumstances (generally in respectively long, thin combustion chambers containing pressurized fuel/oxidizer mixtures), the flame front can exceed the speed of sound, as does the flame front of high explosives, classifying it as a [http://en.wikipedia.org/wiki/Detonation Detonation]. This transition from subsonic to supersonic can create an immense pressure spike that has damaged even well-constructed metal chambers, and is certain to cause a PVC chamber to fail.

It is the goal of anyone who constructs a [[hybrid]] launcher to avoid DDT. It is thought that a short, fat (theoretically closer to spherical) chamber is less likely to incur DDT than a long, thin chamber. Using oxygen enriched mixtures or exotic fuels such as acetylene increase the risk of DDT.

For more information on DDT, try [http://www.google.com/search?hl=en&q=deflagration+detonation+transition&btnG=Search Google].

Hybrid cannon

2007-10-23T07:56:12Z

Pete Zaria:

[[Image:hybrid.jpg|right|thumb|300px| A very well constructed hybrid cannon]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher pressure and temperature gases generated by a hybrid combustion.

A hybrid launcher consists of seven basic elements:

*High pressure combustion chamber
*Pressure-triggered main valve (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually schrader or quick connect)
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, [[pressure gauge]]s and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], flyback, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is the most dangerous type of launcher that can be built. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]) such as Sch. 80 PVC, or even better, metal pipe and fittings. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must, and the limit of a 4x propane/ 4 atmosphere mix should never be breached when using any type of plastic pipe. If a higher mix is attempted, DDT (deflagration to detonation transition, where the flame front exceeds the sound barrier in the combustion gases) can occur, causing an extreme pressure spike. No plastic pipe can handle this pressure spike, and will probably shatter, launching plastic shards everywhere. A chamber made of steel, iron, or aluminum can survive higher mixes than 4x propane/ 4 atmospheres, and have been used at up to 8x propane/ 8 atmosphere mixtures. However, utmost care must be taken with these launchers, in construction and materials used.

Hybrid cannon

2007-10-23T07:55:36Z

Pete Zaria: Corrected gramatical errors and added formatting

[[Image:hybrid.jpg|right|thumb|300px| A very well constructed hybrid cannon]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher pressure and temperature gases generated by a hybrid combustion.

A hybrid launcher consists of seven basic elements:

*High pressure combustion chamber
*Pressure-triggered main valve (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually schrader or quick connect)
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, [[pressure gauge]]s and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], flyback, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is the most dangerous type of launcher that can be built. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]) such as Sch. 80 PVC, or even better, metal pipe and fittings. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must, and the limit of a 4x propane/ 4 atmosphere mix should never be breached when using any type of plastic pipe. If a higher mix is attempted, DDT (deflagration to detonation transition, where the flame front exceeds the sound barrier in the combustion gases) can occur, causing an extreme pressure spike. No plastic pipe can handle this pressure spike, and will probably shatter, launching plastic shards everywhere. A chamber made of steel, iron, or aluminum can survive higher mixes than 4x propane/ 4 atmospheres, and have been used at up to 8x propane/ 8 atmosphere mixtures. However, utmost care must be taken with these launchers, in construction and materials used.

What is a spudgun?

2007-10-23T07:24:23Z

Pete Zaria:

'''Spud guns''', '''potato cannons''', '''produce accelerators''', or '''weapons of mashed destruction''' are all names for recreational launching devices, usually made of common plumbing pipe.

There are two common means to launch projectiles from a spudgun. The [[pneumatic launcher|first]] uses the energy stored in a compressed gas and the [[combustion launcher|second]], more common method, uses the energy released by combusting fuel vapors.
Also, there exists a rare mix of pneumatic and combustion launchers, a [[hybrid launcher|"hybrid"]], that combusts a pressurized fuel-air (or fuel/oxidizer) mixture.

The object of any of these varieties of spudguns is to propel projectiles in the direction of a designated (safe) target, for recreation and sometimes science experiments.

Common [[catogory:projectile|projectile]]s include: [[potato]]es, (obviously), [[mandarin orange|mandarins]], [[tennis ball]]s, [[golf ball]]s, bb's, airsoft, or marbles.... in fact, pretty much any spare vegetable or commonly available object you can ram down the barrel. This is part of the beauty of spudguns.

Some spudguns are very simple, inexpensive designs, such as the aerosol-spray-powered combustion or ball-valve and bike pump operated pneumatic. Some can get complicated and/or expensive, such as large home-made piston valved pneumatics and propane metered combustion guns. A decent potato gun can be built for as little as $15 or $20 at the local hardware store. Some people have spent thousands.

When proper safety is practiced, spudding is no more dangerous than other common hobbies, such as model airplanes. Though as with any activity that can be dangerous, safety should always be your number one priority. So please, take the time to read our [[safety]] section.

[[category:Concepts]]

Fuel meter

2007-06-07T06:26:38Z

Pete Zaria:

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:
*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.

It is possible to construct a fuel meter using only a meter pipe, pressure gauge, and two ball valves (with no regulator). This type of meter is less expensive and will provide accurate fueling, but is not as easy to use as a meter setup with a regulator.

===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 [http://www.burntlatke.com/calc.html performance calculators page]) automates the fuel meter calculations.

[[Category:Accessories]]