Mowing the farm
|2011 Ford Raptor||0.005||0.005||0.276|
|2012 Fiat 500||0.016||0.010||0.192|
|Ryobi 4-stroke leaf blower||0.182||0.031||3.714|
|Echo 2-stroke leaf blower||1.495||0.010||6.445|
It's no surprise that a two-stroke engine puts out more pollutants than a four-stroke engine, what's surprising is the staggeringly huge difference. Do these numbers sound too ridiculous to be true? Let's look so we can see for ourselves.
The source is an independent study done by Edmunds. They don't sell cars or lawn equipment, they aren't political lobbyists, they aren't making a statement about global warming, and they have nothing to do with Kona coffee farming. Edmunds cares about evaluating cars. The point of this study was to investigate the rumor that the emissions of today's cars are cleaner than lawn equipment. As it turns out, the rumor is very true.
An internal combustion engine works by combining fuel with air, compressing that fuel/air mixture so it will burn better, using the resulting combustion to spin a crankshaft, then discharging the exhaust and starting over again. Out of these four phases, called strokes, only the combustion stroke produces power, the other three create drag. This is no big deal because most engines use multiple cylinders that take turns producing power. If you stomp on the gas pedal and rev your engine to 6000 RPM, each cylinder is producing power 3000 times per minute.
Smaller engines sometimes use only two strokes. This means there is only one stroke producing drag instead of three. An engine with less drag sounds like it would be far more efficient. Indeed, two-stroke engines almost always produce more power for their size. This isn't so much because of the fewer strokes as it is because of fewer moving parts. A simpler engine can be smaller and lighter which in turn gives it a higher power-to-weight ratio.
This is great for things like weed-whackers, leaf blowers, and chainsaws. Try carrying a weed-whacker around all day and you'll quickly realize that every ounce matters. You need plenty of power to cut through those thick weeds but you want the engine to be as lightweight as possible so you can carry it. Another advantage of two-stroke engines is that they can operate in any orientation, even upside down. That's great for things like chainsaws.
So what's the trade-off? Pollution. All engines need to burn fuel and spit out the exhaust. In a four-stroke engine, intake and exhaust happen separately while in a two-stroke engine they happen at the same time. That means some of the fuel coming in will go straight out the exhaust without being burned properly. It also means some of the exhaust doesn't leave like it should so the next combustion is dirtier. Even worse, two-stroke engines mix the lubricating oil right in with the fuel which creates all sorts of extra pollutants.
Imagine trying to eat a watermelon super fast. A four-stroke engine goes slow; biting, chewing, swallowing and spitting out the seeds without making a mess. By comparison, a two-stroke engine only cares about speed and is going so fast it carelessly spews out bits of watermelon all over the place.
Two-stroke engines are useful when being lightweight is important. In addition to hand-held tools like weed-whackers, leaf blowers, and chainsaws, two-stroke engines also work great for lawnmowers, small outboard boat motors, small motorcycles, mopeds, go-karts, remote control airplanes, or pretty much any application where being lightweight is more important than low emissions.
Even if you believe that global warming is some kind of complex hoax, we can all agree that pollution is a real problem. As a result, two-stroke engines are becoming less and less common. Nobody likes hearing their neighbor's leaf blower early on a Sunday morning and nobody likes smog. Breathing too many exhaust fumes can be dangerous. Luckily, advancing technology has helped make four-stroke engines smaller and cheaper. There are almost no two-stroke motorcycles or outboard engines left. It's even possible to purchase four-stroke leaf blowers, weed-whackers and chainsaws.
Unfortunately, four-stroke engines are still and probably always will be heavier, more complex and more expensive than their two-stroke counterparts. This means that when an uneducated or budget conscious Kona coffee farmer is buying a new weed-whacker, he or she will probably buy the two-stroke one because it's cheaper and lighter. My weed-whacker is a cheap two-stroke model. Though if I used it regularly I would upgrade to a four-stroke model.
A four-stroke engine in a pickup truck and a two-stroke engine in a weed-whacker are so different that it's nearly impossible to make a fair comparison. Edmunds did their best though. They used a leaf blower instead of a weed-whacker so they didn't have to worry about variable loads like tall weeds versus short weeds. They tried to make the leaf blower follow the extremely thorough protocols for measuring vehicle tailpipe emissions. To top it off, they compared a truck, a small economy car, a two-stroke leaf blower and a four-stroke leaf blower.
It wasn't surprising that the two-stroke engine produced more emissions than the four-stroke engines, what was surprising is exactly how much more. Another surprising result is that the economy car produced more emissions than the high-performance pickup truck. Yes, the pickup did better than the economy car. That doesn't seem right until you understand why.
It turns out that the truck was cleaner because it had more capable emissions control equipment installed. In fact, this equipment is so good that the air coming out of the truck was actually cleaner than the air going into the truck. At least it was cleaner for the types of emissions regulated by the EPA. And this is where things get complex.
The test shows three types of emissions: NMHC, NOx, and CO. The first, NMHC, is non-methane hydrocarbons which is basically the unburned fuel. The Nitrogen Oxides, NOx, create smog, acid rain and ground level ozone. Carbon Monoxide, CO, is an odorless, colorless gas that can kill you if you breath too much of it. All of these are dangerous, both to our health and to the environment, which is why these types of emissions are regulated.
All modern cars have equipment to control emissions. The most important thing cars do is make sure the engine burns the fuel correctly. Beyond that, modern cars use things like catalytic converters which act like a chemical net to catch the bad stuff before it exits the tailpipe. That's why the air coming out of the truck was cleaner than the air going in, because the fancy emissions equipment actually cleaned the air.
Of course none of this applies to a leaf blower or weed-whacker. Even the four-stroke versions don't have the fancy emission equipment that a modern pickup truck has. That stuff is simply too heavy, too complicated and too expensive for hand-held equipment.
When you realize how much pollution is created by weed-whackers, it becomes clear that they are not a very good solution. It's oddly ironic that the "organic" farms are the worst polluters. A giant diesel tractor plowing thousands of acres produces far less pollution than a single small farm running a weed whacker on a few acres. When you consider all the Sunday morning lawn equipment in a crowded suburb, you can see why more and more cities are trying to outlaw this equipment.
In your backyard, the best solution is to grab a rake instead of a leaf blower. On a Kona coffee farm, the solution isn't so easy. I've worked hard to make as much of my farm mow-able as possible. My John Deere diesel mower may not be as clean as a highway vehicle but it's still far better than a weed-whacker. Even if you don't care about pollution, can you imagine trying to weed-whack 13 acres? Not fun.
Of course mowing isn't all rainbows and unicorns either. When I accidentally mow a rock, run over a burlap bag, drive into a ditch, or simply get tired of spending yet another hour riding back and forth across the farm, I have to remind myself that in comparison, mowing really ain't so bad. It sure beats carrying around a noisy, stinky, weed-whacker or sitting in an office every day.
Mowing Kona Earth is easier than most Kona coffee farms but still far more work than mowing a suburban yard. I could hire someone to do this work but I choose to do it myself. To give you an idea of what's involved, I made a video. It's an entire season's worth of mowing condensed into 15 minutes.
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