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Nissan variable-compression gas engine: Is diesel obsolete?

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Nissan revolution: could new petrol engine make diesel obsolete? - Business Insider

ATSUGI, Japan (Reuters) - Japanese automaker Nissan Motor Co has come up with a new type of gasoline engine it says may make some of today's advanced diesel engines obsolete.

The new engine uses variable compression technology, which Nissan engineers say allows it at any given moment to choose an optimal compression ratio for combustion - a key factor in the trade-off between power and efficiency in all gasoline-fuelled engines.

The technology gives the new engine the performance of turbo-charged gasoline engines while matching the power and fuel economy of today's diesel and hybrid powertrains - a level of performance and efficiency the conventional gasoline engine has so far struggled to achieve.

The turbo-charged, 2-liter, four-cylinder VC-T engine averages 27 percent better fuel economy than the 3.5-liter V6 engine it replaces, with comparable power and torque. Nissan says the new engine matches the diesel engine in torque – the amount of thrust that helps determine the car's acceleration.

The engine is also cheaper than today's advanced turbo-charged diesel engines, Nissan engineers said at the briefing at the company's technical and design center in Atsugi, south of Tokyo. They said it should also meet nitrogen oxide (NOx) and other emissions rules in certain markets without requiring costly treatment systems.
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Ugh, clueless reporters - it can't make diesel obsolete. Diesel "works" for both technical (greater torque output at lower RPM) and economic reasons. While variable compression may overcome diesel's technical advantage, it doesn't overcome the economic advantage. Most people don't seem to understand the economic reasons because they hate the oil industry and never bother learning anything about oil.

A barrel of crude oil is a mixture of all sorts of different chemical compounds. When you refine a barrel of oil, you're more or less separating out these compounds. The light stuff is things like natural gas, kerosene (jet fuel), propane, naphtha (used for making plastics). The medium stuff is things like gasoline, heating oil (same thing as diesel), light machine oil. The heavy stuff is things like thicker lubrication oils, bunker oil (used by cargo ships), waxes, asphalt. (The total volume of materials you get after separation is slightly more than one barrel because of the way density and volume works. Real engineers do calculations based on mass for this reason.)

Different types of crude produce different amounts of these materials. The light crude you get from the U.S. Gulf states, the North Sea, and the Middle East produce more of the lighter materials. The thicker heavier crude like you get from Alaska and Venezuela produces a higher proportion of the heavier materials. The oil companies always prefer the lighter crudes, particularly the sweet kind (low sulfur) since it's ideal for converting into gasoline and diesel.

So the proportion of the materials you get from crude oil in first-pass (lowest cost) refining is fixed depending on the crude you're starting with. In other words, each barrel of crude becomes x gallons of gasoline, y gallons of diesel. You can't magically turn a barrel of oil into all gasoline, no diesel. At least not directly. It's possible to cook the stuff longer during refining, breaking the longer molecules into shorter ones. This results in more of the lighter materials, but at greater cost of refining. The bottom line is that unless while there is some flexibility in the amounts of gasoline and diesel you can produce (and it's easier to shift to more gasoline production than more diesel production), it's cost-prohibitive to produce all gasoline, no diesel.

So the current mixture we have of gasoline cars and diesel trucks is pretty much the best least-cost solution to the refining process. You use the least amount of energy during refining and get an x:y ratio of gasoline to diesel. If the fuel consumption of cars to trucks is also x:y, then you can produce gasoline and diesel at the lowest refining cost while still exactly matching demand.

- If gasoline consumption decreases, well you can't convert gasoline into diesel (in fact that's the reason the gasoline internal combustion engine was first invented - as a way to get rid of this "waste product" from the oil refining process called gasoline). So the price of gasoline drops relative to diesel. This is why when the economy is bad, diesel tends to become more expensive relative to gasoline. In a bad economy, people tend to stop driving their cars as much, but they still have to heat their homes and trucks still have to drive because they're moving commerce around. So demand for gasoline drops a lot more than for diesel, and the price of diesel rises relative to gasoline.

- If gasoline consumption increases, the cost of gasoline increases relative to diesel. Not just because of higher demand, but because to produce that additional gasoline requires increased refining costs. Or put another way, a technology like variable gas compression can't kill off diesel. The more successful it is, the cheaper and more attractive diesel will become as a vehicle fuel. (Diesel cars are a drop in the bucket though. The vast majority of diesel is used by big rig trucks and as home heating oil. That's what you should be focusing on cleaning up if you really hate diesel, but it's rare to find an environmentalist who'll study how the oil industry operates in enough detail to understand things like this.)

In my case, I picked diesel to (1) avoid the 2x per year gasoline price spike caused by California regulators not giving the refineries enough time to clear old stock when switching from winter blends to summer blends, and vice versa. And (2) to avoid government (California) mandates to mix corn ethanol into all gasoline. I don't have a problem with ethanol per se, but corn is a terrible crop for producing ethanol. if the corn lobby weren't involved, we'd probably be using sugar beets to produce ethanol - they produce roughly twice as much ethanol as corn per acre of crop.
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