At high speeds and high engine loads (left), the butterfly valve is wide open, enabling air to flow freely into the cylinder. At low speeds and low engine loads (right), the butterfly valve is partially closed, creating an air velocity differential between opposing sides of the cylinder. That differential is responsible for “variable swirl,” seen in the right side of the diagram. (Source: GM)
I think diesel engines should be a first priority for auto makers to get high mileage. The new VW boasts of 50+ mpg. This is without plastic cars and large electric batteries. What are they withing for?
The actual swirl meter package utilized the actual cylinder head, or a solid model, and a cylindrical section below that was the same diameter as the engines cylinder. The sensing was done by measuring the torque produced in a section of "Hexcell" material that was held in place of the piston. The height could be varied in a calibrated and repeatable manner to simulate various piston heights up to TDC. Airflow was delivered by a well calibrated blower system.
IT was not a perfect system, but it was certainly possible to determine exactly how much angular momentum the entering airflow had, which allowed for optimizing the cylinder head profile. We never got called on to make changes, so I never found out how useful it was. BUt their purchase did include a complete set of drawings of all the parts, and the assembly. So there could be a few of those machines around. Most customers did not purchase the drawings and design rights to machines, and we never sold another one to anybody else.
Way back, around 1988 or possibly 1989, I designed a swirl meter for a major US automaker. They had discovered some large benefits while doing some experiments with swirl, but they had no means of reading the actual swirl velocity beyond "more" and "less". So I came up with the concept and our company built the device for them and they were quite happy with it. So based on the discussions that we had in those sales meetings there is definitely a benefit in having enough swirl in the combustion area.
The variable swirl implementation makes a lot of sense because producing that much swirl in very large amounts of air is work, which work done in running the engine is not available to drive the vehicle. So the whole concept makes a good deal of sense. So it does not seem like hype.
Maybe I am listening too fast. Diesel engines are defined as compression ignition, thus they run 'unthrottled' as described. If you 'throttle' the intake, you reduce the volume of the intake air, thus the combustion chamber pressure goes down and compression ignition becomes difficult. Virtually all small and some larger diesels use a pre-combustion chamber which is where the glow-plug lives and where the fuel is injected, this is required because the smaller engines tend to run lower compression ratios. Common rail fuel systems allow the fuel injectors of a diesel engine to meter fuel into the combustion chamber over a longer period in order to enhance combustion, reduce combustion temperature and noise. My point is "Variable swirl" sounds a great deal like American Hype with little basis in engineering. There have been great strides made in diesel engine technology in recent years with U.S. companies being well represented. I hope this is another one, but based on prior advertising hype I am sceptical.
GTOLover, I too have been quite impressed with Diesel rentals in Germany, and like you I am leery of the economics here in the US. In Europe, diesel fuel is considerably CHEAPER than gasoline, the opposite of the situation in the US. This is greatly influenced by politics; both areas try to burden the commercial user (based on the flawed theory that "they can afford to pay it" not recognizing it's ultimately paid by the consumer), and favor the consumer. Since diesels predominate in Europe, that fuel is taxed less, and gasoline more. In the US, with commercial users primarily diesel, and consumers mostly gasoline, the tax/subsidy setup goes the other way. From my point of view, the better solution is to not use tax structures to "tilt" the market, and let the two fuels compete on a level field.
I do remember the earlier GM diesels; the president of an old employer had a 1980ish Cadillac Seville diesel that he truly loved (why, I have no idea, but he actually paid to have the car completely rebuilt after a disagreement with a large deer at 60MPH). It spent more time in the shop than on the road... and was recalled several times to boot!
High-MPG diesel-electric hybrids were the focus of the Partnership for a New Generation of Vehicles in the 1990s. Each of the Big Three automakers produced a diesel hybrid that achieved 70 - 80 miles per gallon. Unfortunately, most U.S. consumers weren't particularly interested in high-MPG vehicles in the late 1990s - early 2000s, and the federal government pulled the plug on the project when the new administration took office in 2001.
Eventually they will mix the two and break the 100mpg mark. When you add in Hybrid drive and CVT you take out the problem areas of the rpm T curve and the efficiency goes through the roof. Diesel idles at near zero fuel consumption so you don't have to keep starting and stoping the engine like a gas engine.
I have been saying it for years, ever since they made the announcement back in 2008ish, when GM was I designing a smaller diesel engine for the medium duty trucks. I think it would have taken of then. People want power, and fuel economy, the diesel power plant brings the best of both worlds.
So I pull-up to the pump and see diesel is $3.90 a gallon and gasoline is $3.40 a gallon I am pretty sure I am buying gasoline. A diesel that can get 46 mpg is good, but why not buy a gasoline hybrid?
Then we have the whole late 80's early 90's diesel nightmare tarnishing US consumers view of diesel automobiles. I am not sure that the US is ready. They will sell OK as a small share of the diesel car market, but I do not forsee the Cruz overtaking the gasoline version. The diesel costs a little over $25k and the ECO (at 42 mpg) is a little over $21k. May not seem like much, but most consumers will not calculate the difference and go for the cheaper car that uses cheaper fuel.
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