Dec 22

Home for Christmas (or: diesel vs gas)

Tag: boat work,energy efficiencymattholmes @ 10:10 pm

I grew up on a farm, and all my life my father has been bashing gasoline engines and lauding diesels. He wouldn’t buy any vehicle that wasn’t a diesel, and we had two 1,500 gallon diesel tanks around by the barns–one for on-road vehicles and one for the tractors. As a result, I grew up plugging the diesel suburban into an extension cord in the winter, and waiting to start the car until the glowplugs–whatever the hell they were–warmed up the engine. Meanwhile, in their gasoline vehicles, my friends could fill up at any gas station and accelerate from 0-60 in something significantly less than the 30 seconds it took in the suburban. I wrote off my father’s opinion as old-fashioned, ultra-conservative, non-progressive, and wrote off our diesel vehicles as too loud, too much work, and too slow.

I’m home now, back around my dad, and back into the diesel debate.

Never in a million years would I have guessed that one day I would know how to sail (?), that I would own a sailboat (!?) and that the sailboat happens to CONTAIN A DIESEL ENGINE (!?!). And never ever ever would I have guessed that one day I would agree with my father about the benefits of diesel engines. Don’t be mistaken: I have done my own research and come to my very own, independent conclusions. They just happen to be the same conclusions as my dad’s.

This being the holidays, time for family reconciliation, good will, etc etc, I am hereby rising above my stubborn mindset for the past three decades to admit that my father was right: diesel engines are more efficient and longer lasting than gasoline engines.

Most people don’t understand the difference between diesel and gas–that was my problem. As a result of this ignorance, nearly all americans drive less efficient, less reliable, shorter-lived vehicles while all of the countries in the rest of the world drive way more diesel vehicles than us.

These are the facts: diesel fuel has more energy per gallon than gasoline, and diesel engine are more efficient at extracting that energy than gasoline engines. As a result, diesel engines get 20-40% better fuel economy and emit 10-20% less greenhouse gas than gasoline engines1. Moreover, the nature of burning diesel requires diesel engines to be more robust than gasoline, and as a result they last much longer on average than gasoline engines.

I’ll lay some details of the mechanics: the difference between the engines is in how the fuel is ignited. In a gas engine, a spark plug actually lights the gas on fire at a particular point of the compression. In a diesel engine, just the force and heat of the compression of the piston ignites the diesel; a diesel engine doesn’t need/use spark plugs.

In the engine cylinder, diesel fuel burns whereas gasoline explodes. Diesel fuel burns steadily as it expands in the cylinder and turns the drive shaft; gasoline explodes for a short duration as it gives the drive shaft a jerk. As a result, gasoline engines have rapid acceleration, but low torque. With the slow burn, diesel engines pull like a horse, but they won’t leap out of the starting gate.

In order to ignite the diesel via sheer compression, the engine must have a higher compression pressure than a gas engine. Consequently, the engine itself must be stronger and more durable than a gas engine. It is because of this beefier construction, and the fact that the diesel burns steadily rather than explosively, that diesel engines last so long.

Diesel engines have come a long, long way technologically in the past few decades, particularly in one area: cleanliness. Environmentalists could not advocate the diesels of 30 years ago because the exhaust was too dirty. Even though they emit less carbon dioxide than gasoline engines (always have), they used to be so dirty that it offset the carbon dioxide advantage. Modern diesel engines use an array of technology to be more clean, and in the process became even more fuel efficient.

Today’s diesel engines represent an immediate, proven way to reduce america’s wastefulness and impact on the environment. A number of studies, including from the DOE, testify to the environmental benefit of adopting diesels. They win awards, and get lots of attention. Which is one reason why we will be seeing so many diesel offerings from car makers in the next few years . . .

Enough of the proselytizing–I’m sounding like my father. How does this relate to our engine situation?

I regret to admit that our engine is very certainly old technology: 30 years old, to be precise. The old technology is both good and bad for us. It is less efficient than modern engines, and much dirtier. On the other hand, it is as simple as a diesel engine can be, which means that novices like us actually have a snowball’s chance in hell of understanding and working on it. Modern diesels are computer controlled, and have high-tech add on components, none of which I understand.

Our engine emits white smoke, which means that it isn’t burning the fuel efficiently. It needs to be addressed, which may mean a relatively simple tune-up but likely means a whole lot of work and unforeseen expense. With the help of a great diesel friend and regular phone calls to my dad, we will be tackling the engine in the upcoming months. Stay tuned for more diesel details.

4 Responses to “Home for Christmas (or: diesel vs gas)”

  1. Laureen says:

    Great post! Thanks for breaking it down like that. Freak that I am, though, and cutting-edge guys that you are, I’m wondering if you’ve though about biodiesel (what does Dad think about that?) and if you’ve thought about taking The Big Leap ™ and moving to electric? With the new numbers out for Peak Oil (Monbiot has a great tirade going about it), I wonder how much longer the debate about *which* kind of fossil fuel can be sustained, before it becomes a debate about how to repower entirely…

  2. mattholmes says:

    The research I have done suggests that biodiesel is better than petrodiesel in some ways, worse in others. The energy content is 9% less than petrodiesel, so you need to burn more of it, the NOx emissions are worse, and the sulfur emissions are better. The carbon emissions are identical (at the exhaust). People make claims about how biodiesel greatly reduces carbon emissions, but the claims are all based on the production side of things, not the actual amount that comes out of the exhaust pipe (which is actually greater, since you have to burn 9% more of it to go the same distance as on petrodiesel) So it is unclear how it comes out, in the balance, on the burning side of things. It happens to be better for the engine (better lubrication). On the production side of things, we can make it here at home out of soybeans (which is currently the most efficient crop for biodiesel production in the US). Unfortunately, the debate is almost a moot point, because the data I’ve seen suggests that even if we converted all of the arable land in the US to growing soy for biodiesel production, we would still only come up with a tiny fraction of what we need. My dad grows soy and sells it as part of a farmer’s brokerage consortium, and he said that they came close to getting into it when fuel hit $3/gallon, but it is not profitable below that. So it is exciting, but not yet a practical answer. There are promising possibilities in the works, including the use of algae (which might even eat waste as food) to increase yield by 30 times the current efficiency we get from soybeans. Like you said though, as far as the environment is concerned we really need to be looking into repowering without fossil fuels entirely, because both petro and biodiesel pump nearly the same amount of carbon dioxide into the environment either way.

  3. Borg says:

    Most of these “facts” are not facts. Diesel engines are much worse than gasoline for environment. Instead of reading few VW sponsored magazines read scientific FACTS:
    Also at the same compression ratio gasoline is MORE efficient than diesel, and to get 1l of diesel you need 25% more oil. Diesels also need to have motor oil changed more frequently, and are nightmare for service. It may last 2x as gasoline but money you put in servicing costs more than 3 new gasoline engines in same period of time 🙂

  4. mattholmes says:

    whoa there, it appears that you can support anything if you scour the internet long enough. The europeans are meeting higher emissions standards than we are, and doing it with diesels, if you want to sift through the details:

    Also, this “money you put into servicing”: do you personally own a diesel? Because I have personal knowledge of what it costs to service an old diesel versus buying a new gasoline vehicle, and from personal experience I can assure you that it’s better to fix your old than buy a new. Also, I have personally changed my own oil on both gasolines and diesels, and you select the oil for the application and you change it at the same intervals.

    I don’t just have facts, I have direct experience with both types of engine–you can consider me a primary source if you like. I grew up on a farm and was exposed to a dozen diesel engines and a half-dozen gasoline engines. I grew up in a family where we counted our mileage and the gallons of fuel/gas to check gas mileage, and where we did all our own work on the vehicles. Our diesels outlast the gasolines and have cost significantly less, both to maintain and in lifetime cost. Sounds like you’ve been overly affected by the pressures of our consumer economy. True, diesel engines aren’t all roses–in ways they’re definitely dirtier–but the marvels of modern technology have brought cleaner diesels, and new regulations will further ensure even cleaner diesels as the US is forced to adopt new nitrogen capture exhaust technology.

    And next time, if you want me to accept your comment, put your real name and take ownership of your comments, and not some phony link.

Leave a Reply