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CNET On Cars: Car Tech 101: Understanding diesels
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CNET On Cars: Car Tech 101: Understanding diesels

6:03 /

Scorned in the U.S. and adored in Europe, diesels have the unfair tag of being dirty and inefficient. They are, however, quite the opposite.

-The first experimental engine was built at Augsburg in Germany during 1893. [unk] people were convinced that no machine would work at a high pressures, which diesel insisted were necessary-- -Now let's start our little journey into diesel learning. Here in an unusual diesel, this is the Chevy Cruze diesel. Not only are diesel's rare in America but this one is made by an American company. They can get twice as rare. But the principles are the same. A diesel engine starts this combustion cycle by compressing air and just air highly 22 to 1 can be as much of a compression as you find in here. Compare that to a gas engine around 8 or 9 to 1, so it's night and day. And at the very top of that compression cycle, the diesel fuel is injected and it all combust spontaneously because the temperature is so high because the pressure has been raised so much. There are no spark plugs. That's how a regular gas engine gets combustion going. But these guys do it spontaneously by piece. Then, at the very last minute as that piston comes up and compresses the hell out of that air. What happens then is this blast of power. It's a really high explosion because of that high compression rate and you get that characteristic knock related to that whole idea of spontaneous combustion. So notice that one of the key timing factors that makes the diesel run well is the timing of that fuel injection as suppose to the timing of a spark. That's why very precise direct high-pressure injection is the key to these motors in the modern era. Also because they compress their charge so much before combusting, they tend to ring more out of the fuel up to 50% of the energy in a droplet of diesel. Gasoline cars don't do nearly that well. Now, if you think diesels are noisy, stinky and slow, you're probably over 40. Old enough to remember when they were. Modern diesels like a Mercedes GLK, a Volkswagen Jetta TDI or even the Chevy Cruze are none of the above. And there are 3 important technologies you can thank for that. First off is common rail direct injection. The common rail part means you've got this metal plating or basically pipes that has the fuel pumped under extremely high pressure up to 29,000 psi. From there, it is direct-injected into the cylinders with extreme precision partly because it has that high pressure behind it and partly because they're not using Piezo electric injectors, which open and close extremely quickly, sometimes multiple times in one combustion cycle. Precise injection means better use of fuel, lower emissions, more power, better economy. Win, win, win, win, win. The second big tech trick is turbo-charging. This complex turbo-charging is the key because the diesel without it will tend to bunch up all its power down at the bottom of the tech. What the turbo does is up to spread the power further up to the RPM range and get it delivered faster. Get it off the line quicker. These things are not slugs anymore. That's an old school idea. The last technology trick is exhaust scrubbing. This Mercedes, for example, uses urea injection. Urea fluid is vaporized and spread into the hot exhaust, which catalyzes it to convert those nasty nitro oxides into pretty benign water vapor and nitrogen. Secondly, there's additional sort of cooking of the exhaust, hot catalyst downstream actually re-cook it a couple of times in some cases to cause a chemical reaction that also reduces the nasty stuff coming out of the tail pipe. And thirdly, ultra low sulfur diesel fuel has become pretty much the rule of the US, Europe and many other areas. By not having so much sulfur, it is a neatly cleaner and by not having so much sulfur, it does it-- now the other 2 technologies I just mentioned allowing them to work. Now I could talk to you about high compression ratios in common rail injection and blah-blah-blah. It's a little [unk] in the face. But all you really wanna know is-- does the diesel car drive and feel like a UPS truck? Or is it actually a nice car? Let's go for a ride. I think you're gonna be probably surprise. Now the first thing you figure out on a diesel is the tachometer is different. The red line is much lower. You don't run these cars up this high. There's no reward there like on this Jetta TDI. You can [unk] by 4,000 and basically game over. It's time to shift. These are low-end grunt engines compares to a gas motor. And even if you do, run them out. There's not much payoff, which is actually a very easy way to drive or just not so much used to it. The torque in the low to low-med is just a delight and it makes every day driving a lot of fun. It's also that kind of acceleration that we all love. You will notice in, really, every diesel I've driven less so at the high-end more at the low-end. But there is a different engine note. There is a diesel rattled that is innately in there and depending on how well the car is isolated and insulated. You will detect more or less of that. You have to get use to that but it's not a bad sound as much as the difference. Beyond that, one of the other things you have to get used to is the back of that damn fuel gauge hardly even moves. Now, I didn't know if this one was broken in this car and you're like driving it for an hour then finally saw it come off the full peg and starts to work its way down. Diesels tend to have tremendous Range 7 or 800 miles is not unusual because they have normal size tanks and can get great long leg highway economy in particular. You know, like you're in the market for a very efficient car and you enjoy the real joy of driving which comes from torque. You owed to yourself to drive a couple of today's modern diesels and see what they are alike. I think diesels have a lot going for them and in many ways they've got better market legs in a lot of the hybrids and highly electrified cars out there.

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