LPG Fumigation

Page Two

Construction of My System:

This page describes the components of a basic fumigation system

But first, a word from the Shark legal department:

OK, now that that's out of the way (can't be too careful these days), we can get down to business.

The Tank and Regulator:

What type of tank you use may depend a lot of what type of vehicle you intend to use it on. If you are adding a system to a large truck or a motor home, you will probably have plenty of room for a frame-mounted horizontal tank. If it's a motor home, you may not need to add a tank at all, just use the existing one, although an additional regulator may be necessary, depending on the type of system you install. The smaller the vehicle, the more difficult the job of finding a suitable location to mount the tank, and the more difficult it will be to find a tank the right size and shape.

Should you be tempted to mount the tank in the enclosed trunk of your car, remember that DOT (Department of Transportation) rules forbid such installations unless the enclosure (your trunk) is well ventilated to allow any seepage or leakage of gas to readily escape. If you want to know how well ventilated it needs to be, go visit a motor home or travel trailer dealership and see how propane cylinders on recreational vehicles are mounted. Unless you plan on wearing a racing fire suit while driving, forget mounting the gas cylinder inside the passenger compartment.

The size of the tank will also depend on your usage. If this is a long-haul truck or RV tow rig, you will probably want the gas on full-time, in which case you will need a sizeable cylinder. For occasional hill climbing or passing on the road, you might be able to get by with a capacity of only a few gallons. Installations in cars meant for racing or speed exhibition will need only a small reservoir of fuel, perhaps with several tanks that can be interchanged when emptied.

During my initial trials, I used a Coleman camping fuel bottle as a source for gas. This picture is posted elsewhere on the site, and has been picked up by several discussion forums as an example of how not to do it (like I always drive around with a propane cylinder balanced on the drive train hump...). The small cylinder was good for about 60 miles of continuous use, but has been replaced by a 1¼ gallon cylinder with a proper shut-off valve. This image also shows the BBQ regulator and 12 volt solenoid valve that I used to test the system. These components will be discussed in greater detail later in this page.

This does bring up an important point. Any containment vessel you choose for your system should be properly and securely mounted to avoid damage to the equipment during driving. Any wiring or plumbing from the tank or associated components should likewise be properly secured out of harm's way.

The regulator you use will depend on how much pressure and flow is needed. The BBQ regulator shown above was perfectly adequate for my purposes on the VW N/A engine, operating at 25,000 BTU per hour. It cost me $2.00 at a salvage yard, and produces 11 inches of water on a manometer (.397 PSI). If your fumigation system will be for a turbocharged engine, or if your engine is of a high displacement, you may want to purchase a regulator that has an adjustable output pressure. Turbo'd engines generally require pressures of 4-6 PSI, at greater flow rates than a household low-pressure regulator can provide.

The 1½ gallon LPG cylinder is securely mounted via a steel ring
encircling the base and a wing nut through the protective top collar
mounts it to a custom bracket. In this photo, I'm trying out an
acetylene regulator. Note the proximity of a fire extinguisher!

A regulator of the type use on oxy-acetylene welding equipment is one type suitable for an LPG system. Just make sure that any regulator you use is rated for the pressure of a propane cylinder (approximately 250 PSI) and is rated for flammable gas duty. Two-stage regulators will be less affected by changes in altitude, barometric pressure and temperature.

Note that systems which demand a lot of vapor will need a regulator which can supply the specified flow without freezing up. At some point, large gas flows will require you to install an evaporator system like those used on LPG fueled spark-ignition engines, and the tank will need to feed liquid LPG to the evaporator/regulator.

The Solenoid Valve:

This piece of gear seems to be the sticking point in many of the LPG systems that I hear about. Essentially a solenoid valve is an electrically actuated valve that is used to control the flow of gas into the engine. It needs to be rated for the pressure that it is being asked to control, and be safe for flammable gases. The electrical rating needs to be 12 volts DC, continuous duty. I was lucky enough to find a valve being offered by a surplus equipment supplier for $5, but their stock in that part ran out. Some research into substitute valves reveals that there are several choices available.

The most common supplier of solenoid valves is Asco. Their general purpose "Red Hat" low pressure valve is catalog # 8262G002. The specifications sheet includes the information that the 12 VDC coil number is 238310-004-D. Presumably, this coil could be ordered separately as a replacement part and installed on any compatible valve body.

W.W. Grainger company also lists some 12 volt DC solenoid valves. This valve is apparently still stocked and available for purchase.

Be aware that these specific valves may not be rated for LPG gas duty. If I were doing it over, I think that I would try to find a purpose-built LPG or natural gas valve from Asco, then purchase the 12 volt DC solenoid coil and fit it to the valve body. Such valve bodies should be easy to find from a gas appliance repair shop or even in a salvage yard. Most likely they will have 120 or 24 volt AC coils, as this is the most common voltage for machine controls. Fitting the 12VDC coil should be fairly trivial.

If anyone comes up with a better source for 12 volt solenoid valves, please drop me a line so that I can update this page with additional information.

Orifice Action:

Metering systems for gas pressure devices generally include an orifice, or jet to control flow. The size of the orifice can be fixed, or adjustable. Fixed orifices must be drilled out to increase the flow for a given pressure, while adjustable units can be manipulated with a wrench or similar tool to change the quantity of gas that passes. Note that adjusting the gas pressure will also effect flow rates. Since my "dump" system utilizes low pressure and salvaged components, I opted to simply reuse the orifices that came with the second-hand gas BBQ grille, and drill the hole for best results.

Here you see two additional jets that I drilled to try out high rates of fumigation. The installed orifice (left) has a #53 drill hole, while the two others have 1/16" and 3/32", respectively (They supplied way too much gas for my engine!).

Supplying Gas to the Intake:

While it is possible to connect the orifice(s) directly to the intake of the engine, I chose instead to locate the jet at the solenoid and supply the metered gas to the engine via a length of LPG-rated rubber hose. The hose is terminated at the intake manifold end by three "T" fittings which distribute the gas evenly to four ports drilled into the air box after the engine's air filter. These ports are nothing more than 1/8" male pipe thread to ¼" hose barb 90° fittings. The intake manifold was drilled and tapped to accept the pipe thread ends of the fittings. The aperture of each port is directly above each of the runners in the intake manifold that supplies air to the cylinders. The ports are visible as the brass fittings at the top of the aluminum manifold air box. Also visible is the 3" air duct which supplies intake air from a cowl scoop mounted on the hood. We will discuss the importance of free-breathing on a later page.

Here's a very simple way to get gas into your engine, but it suffers from the drawback that eventually, your air filter will become coated with an oily film from the LPG. Note that the stock air horn is of a small diameter, and is picking up warm air from behind the car's radiator. See following pages for advice about modifying this intake.

Fumigation introduction on a turbocharged engine usually takes place before the air intake to the turbine, allowing the turbo to help mix the propane with the intake air. Please note, however, that this will mean that your turbo, intake piping, and intercooler (if you have one) will contain a flammable and potentially explosive mixture of LPG gas and air under pressure. Adding the gas after the turbine output is possible, but you will need to account for the boost pressure, raising the LPG regulator to a value greater than the turbo output, typically by 3-6 PSI.

Liquid LPG Systems:

Occasionally, I get messages from people who are interested in knowing if it's possible to supply liquid LPG to the intake of the engine, both for the purposes of fumigating the charge air, and because the evaporating liquid would further decrease the temperature of the charge air.

In response, I can only say that I have not experimented with such a system. The control and metering of liquid propane gas is much more difficult, and requires specialized equipment to which I do not have access. Additionally, the safety aspects of handling liquid LPG are much more strenuous, and any fire/explosion hazard associated with a vaporizing flammable liquid are enough to scare me off!

If this type of system is of interest to you, consider doing some research on methanol injection, it accomplishes the same results with much less complexity and risk!

Next up, learn some self-control!