Next-Gen Mazda2 Will Return 70 MPG, Without An Electric Motor
greencarreports.com
greencarreports.com
The 70mpg figure is from the Japanese test.
The Mazda release said the car would achieve 70 miles per gallon, but that number was based on the Japanese test cycle, meaning American mileage would be lower. A 15 percent increase from the existing Mazda 2 would result in a combined 37 m.p.g. (For comparison, the Toyota Prius, which gets a combined 50 m.p.g. from the Environmental Protection Agency, achieves 89 m.p.g. in the Japanese test.)
More accurate article here:
http://wheels.blogs.nytimes.com/2010/10/21/mazda-next-genera...
Detonation occurs when the pressure and temperature inside the cylinder cause the air-fuel mixture to literally detonate, rather than burn (relatively) slowly and evenly as desired. If this occurs before the spark, it is called pre-ignition. When it occurs after the spark, while the flame front is progressing through the cylinder, it is referred to as detonation. Higher octane fuels are more resistant to detonation and pre-ignition, and usually go hand-in-hand with higher compression ratios.
As a side note, E85 Ethanol has a ridiculously high octane rating, among other things, which allows for higher compression ratios and much higher boost in forced-induction engines. I keep hoping E85 will catch on outside of the corn belt so I can effectively get race gas performance from pump gas in my turbocharged motor, but no such luck yet.
There are plenty of tricks that can be played to reduce the risk of detonation using low-octane fuels in high compression motors. Efficient head design with excellent cooling will reduce cylinder temperatures and minimize hot spotting within the cylinder head, reducing the risks of detonation and pre-ignition. Getting the heat out of the valves is particularly challenging as they only meet the cylinder head in a relatively small contact patch. The valves can be filled with sodium, which turns to liquid as the motor reaches operating temperature and circulates within the valve, cooling the valve and further reduce hot spots (pre-ignition points) within the motor. Also, designing the piston and head to thoroughly mix and swirl the intake charge helps create a quick, even, clean burn.
However, to get up to 14:1 on a production motor, I wonder if Mazda is playing serious games with the intake camshaft timing to reduce the effective compression ratio. If you leave the intake valves open long enough after the piston begins the compression stroke, it will actually push a tiny amount of air back out of the intake valves, reducing the effective compression ratio of the motor at top dead center. With variable valve timing, Mazda could just be doing this near full load, where detonation and pre-ignition are problems. At partial load, you can get away with much higher compression ratios (up to 20:1 in certain cases, IIRC) with associated increases in efficiency (and thus higher MPG).
Either way, I'm glad to see more efficient internal combustion engines. The internal combustion engine is a 100+ year old technology, so significant improvements are hard to come by without drastically increasing the cost of the motor. Good stuff.
Motorcycle engines, with their smaller cylinder sizes and thus lower combustion chamber surface area vs. volume, have a much easier time cooling their cylinders and heads. This reduces hot spotting, making it easier to get away with larger displacements. I'm sure there was a healthy amount of overlap in your cam, since that motor was designed to rev to the moon.
Still, I did have a 14:1 piston in my single-cylinder, 450cc dirt bike motor and ran 91 Octane in it all day long without problems. Granted, I never took it below 4000ft altitude, which probably helped, but the cylinder, head, and valves were all designed for excellent cooling. And I had a really aggressive cam setup.
Either way, kudos to Mazda for pushing the limits here.
You have either never driven a motorcycle or never driven a car with a 1L engine.
Even a 'slow' motorcycle beats ridiculous sports cars in 0-60 times. the suzuki sv650 I rode a while back? it's not a particular sporty bike, but it's rated at 0-60 in 3.7 seconds. You are competing with the tesla at that point, in a vehicle that was less than $6K out the door, brand new.
the geo metro that was my first car? (1 liter, 3 cylinder) it was approaching a 13 second 0-60. It's a completely different experience than a motorcycle. (and costs significantly more if you buy it new.)
I don't understand the Smart car. The Honda Fit costs about the same and has 4 seats or a good deal of indoor space. Probably a style thing.
I switched from a 3/4 ton 4 door pickup to a Honda Fit, and am not looking back. I've got more indoor cargo space in the Fit and don't need to bring a book to read while pumping diesel into the truck. (But I can still borrow the truck the once or twice a year when I need it.)
Seriously, why wouldn't VW and the like bring over ultra efficient cars if they would sell? Reason being is it costs $$$ to license a car for import, to get DOT stamps of approval etc. If sales won't cover those costs, it's a loss for the company.
I've a career in Mech/Auto Eng, so I know it's more complicated than that. Nonetheless, it shows how the car industry can confuse with these headline figures.
I will add that I'd probably rather breathe the exhaust of my Rover (with micron-scale smoke particles) than that of a modern car (with more biologically-active nano-scale particles)
(And the petrol version of his car gets 31.4 US mpg. I blame the US not getting really clean diesel until the mid-2000s for the lack of mini-diesel engine'd cars in the US.)
edit: the US did not get ultra-low-sulfur-diesel as a standard until 2007.
Edited to add: After reading a bit more, I see your point. I guess there have been new studies since I last read that show that per unit of mass, the volatile organic compounds in gasoline exhaust are more harmful, they just have less volume than diesels. Seems to be about a draw.
But diesel in the UK now has 10 ppm sulfur.
In the US it used to be higher than 500 ppm, now its regulated to 500ppm for some vehicles and lower for some other classes.
Starting in 2014 all US will be 15ppm.
Also, soot isn't directly related to sulfur in fuels. It's the suit removing mechanisms in newer diesel vehicles that are ruined by sulfur, so newer vehicles can't run fuel with sulfur in it without incurring a large repair bill. An older diesel vehicle that belches out soot will continue to do so, regardless of sulfur content.
But the VOCs definitely not great. Plus, presumably (I'm guessing), the NOxs from high temp lean combustion in modern gasoline engines are an important factor too?