This project has been two years in planning and implementing but is now completed. What the system does is inject propane into the incoming air stream but before the turbo of a Cummins 190HP diesel engine. The purpose is to accelerate the combustion of the diesel fuel leading to a cleaner engine, exhaust, and increased power. This is not a snake oil proposition. Mr. Diesel himself tested his engine with great success with what was called in his time ‘erdgas’ aka ‘earth gas’, which contains propane, butane and other gases. The process is simple and the gas just helps the diesel burn more quickly and completely, thereby improving horse power and torque. What I did initially was to gather information off the internet on the how and why of this type of process.
It didn’t take long to discover I’d need an electronic circuit to control the gas valve if I wanted the system to behave well. I had been using a simple OFF/ON switch with built in circuit breaker mounted next to the drivers seat. So, after some thought, I designed a circuit that took the various engine monitoring signals, then based on that, decided to either open or close an electromechanical gas valve near the entrance point of the gas in the air stream. Those signals are oil pressure, RPM, and shift lever position. If the oil pressure is to low, I didn’t want to be introducing an accelerant. If the RPMs were below a certain set point and LP was still flowing, that could harm the engine and would use too much gas with not much return. I had seen this problem on a couple of occasions when I’d forgotten to turn off the propane and I’d come to a stop light. Soon I’d feel and hear a labored idle from the engine. Turning off the gas immediately stopped the weird knocking type idle. And if the shift lever was in a low gear to use compression to slow the vehicle on a long hill, I wouldn’t want to introduce gas then either. Here’s where I positioned the circuit under the dash, that small black rectangle with the wires going to it in the lower left is the circuit:
And a close up of the circuit. It’s simple so it’s small, I’ve since installed a ‘capacitance multiplier’ so that large device (a capacitor) hanging outside the box has been removed:
I did have to install a microswitch on the shift lever mechanism, so that the cam action closes the switch when in ‘Drive’ and it is open in all other positions. That took hours as I didn’t have appropriate tools and needed to grind a smooth notch into the rotating disk that is part of the shift mechanism. It is now mounted inside the cabinet next to the drivers seat.
The other signals were available under the dash at the RPM meter in the form of a sine wave of varying frequency, and at the oil pressure meter in the form of a varying DC voltage . Since there were many connections to do near and under the dash, I mounted the circuit there and ran a single wire back to the engine compartment to power the gas valve, using the chassis for ground.
After the circuit was designed, built and wired in place, I mounted the valves and gauges in the propane fill compartment. My house tank has a take off connection for gas BBQ and other items so I used that high pressure connection (depending on temperature, it runs around 100 PSI) and dropped the pressure with an adjustable 0-30 PSI regulator. There was enough room for an input pressure gauge, the regulator and the output gauge in the fill compartment that left enough room so filling the two tanks (the house tank and the genset tank, both take around 25 gallons) would not be an issue. Here’s where I put the gauges and regulator. The first gauge, the one on the right of that red topped regulator, is a 0 to 200 PSI, the gauge on the left is a 0-30 psi:
To keep the area clean, I use a plastic sheet wedged under the assembly and held in place by the closed door. Over thousands of miles the sheet has not tried to escape.
I used copper tubing because the run back to the engine was 25 feet and using acetylene hose, while less expensive and easier to work with, didn’t have the protection from accidental leaks of flammable gas that came with copper. I used flare fittings so to avoid having to use teflon tape in difficult areas where I’d be working. I was able to borrow a flaring tool from a local plumbing supply shop…the guy didn’t even ask for a deposit.
I routed the tubing back to the engine compartment and connected to the gas valve in an area of the compartment that stays relatively cool. Then I used a short piece of acetylene hose to go from that valve to the hole I drilled into the plastic rubber type air tubing that’s just before the turbo. I used a brass hose fitting pushed into the tubing. It’s not moved for a couple thousand miles now. This shot shows the valve and the quick connect as well as the oven thermometer I used to check average temp near the valve, the valve is rated at 180F max operating temp so I needed to stay below that. It does:
After installation of the components, which included wiring in the previously installed Off/On/Circuit Breaker switch, I got on the road and monitored the tell-tale lamps I’d built into the circuit. They indicated that my circuit was doing everything correctly so I pulled over and turned on the gas. The next hour of driving I adjusted the pressure for the best power to cost ratio, stopping and adjusting the regulator setting when appropriate. Propane is generally less expensive then diesel but it still is an expense so I didn’t want to waste it.
A few days after getting the fumigation system installed, I left Mazatlan, and headed north. I fiddled with the gas pressure to get the best boost while trying to conserve propane as I climbed the moderate hills in this part of Mexico. On one really long stretch of mostly flat road, I left the gas ‘On’ as a test of usage and found that by the end of the day, my propane tank was nearly empty. This was also suppose to be a test of diesel mileage improvement, if any, but I cut that test short since it wasn’t likely I’d get more then a 10% improvement anyway (based on the tests of others), and the hassle factor of having to find a propane outlet nearly every day made the test unreasonable. It wasn’t convenient to refill the tank so I didn’t calculate my mileage for that portion of the trip. Later, when I calculated the entire tank, there was a slight improvement in mileage but I can’t call it a successful test as my method wasn’t exacting enough.
I did test the propane injection system on flat stretches and on the several hills. It seemed to work well and gave me some extra boost up those hills, on the flat stretches it’s suppose to save fuel. I suppose it’s adding 50 HP or so to my engines effort so that helped me get up the hills just a little faster. I watched the engine temp closely on the day that I had propane running the entire travel time and found that on long flat roads, and with 85F air temp most of the day, that the water temp gauge only ran about 10% hotter (one to two needle widths increase on the gauge over normal). That was good news since one problem with propane fumigation can be an overheated exhaust system, which can cause broken parts but not much else, according to what I read. But there have been cases where too much propane has been used and caused a meltdown of the engine. I saw an on-line video of a diesel 4-wheeler smoking the tires for a few seconds before the engine blew, so I spent a lot of time watching that temp gauge and guesstimating the amount of propane I needed, which I can adjust with the adjustable regulator. Of course I needed to stop the rig to do that, but I expected that once I found the sweet spot, I wouldn’t be adjusting it much after that. I tried to be cautious because my engine is 13 years old and over stressing it at this age isn’t the best idea. But I do want more horse power to get me up the hills a little faster so I checked several flow rates, usually adjusting upwards, settling on what seems to be a good compromise between added power and my sweat level regarding the engine life.
Now that I have several thousands of miles on the propane injection system, I’ve discovered a few things about it that I’d like to share. IT WORKS! I do get an increase in power when I’m heading up a hill and throw the switch. I’ve been trying to find the best trade off between power and safety so haven’t settled on an exact pressure yet and I’m not sure I ever will so for now I’m running it a few PSI below the maximum setting of the flow control.
Originally, I thought that my electronic controller would be all I’d need to automatically adjust to changing road conditions but I’ve since found out that I need to add more circuitry to sense when the rig is heading up a hill. That is needed because I found that I would have to manually turn it off to often when I’m driving in hilly country. The gas isn’t needed when on the flat so there is no need to leave it on but my automatic circuitry does just that. Circuitry to sense a rise in the road isn’t a challenge so I should have that portion designed and installed by the time I head back to the lower 48 (I’m in Alaska now).
Naturally, this system hasn’t turned the rig into a race car but it does make it charge up hills faster and with less loss of speed. For instance, before the system, if I was heading up a 3-4 % grade for a few miles, it would slowly lose speed until I’d be going 35 or so when I got to the summit, with the fuel peddle all the way to the floor. Now with the injection system, I’m usually still going 55 when I get to the top with room under the peddle, or maybe I’ve slipped down to 45MPH if it’s steeper. Still much better then the 35 or 25 it use to drop down to.
Overall, I’m pleased with the results, and if I ever get a huge chunk of money, I’d take the chance and boost the pressure way up to see if I can go 60MPH up a 8% grade, to hell with the engine. Until I get that huge chunk of cash, I’ll just take it easy and run it at what seems to be a safe pressure (I’ve detected very little engine heating by the system).
One of the things I’ll need to keep an eye on is that if overheated, and that’s a possibility since the propane supply must run back into the engine compartment, propane can ‘crack’ (as in petrochemical refining). This is when heavy end residuals or ‘heavy ends’ break off the molecules and become oily or waxy like residues that can clog the lines or regulators. The temperature where this can happen is usually given as above 130°F. That temp is easily reached on a warm day in the engine compartment. I am using propane gas as opposed to liquid so that problem should not appear, but it’s something I’m keeping an eye on.
Meanwhile, I’m considering developing a kit of parts to sell to other diesel pusher owners who might need a little more power. The installation would be easy for a qualified tech, most of the wiring needs to be done around the dash, simplifying things, and the propane plumbing and control is straight forward and simple.