

Next-Gen Mazda2 Will Return 70 MPG, Without An Electric Motor - coreyrecvlohe
http://www.greencarreports.com/blog/1050675_next-gen-mazda2-will-return-70-mpg-without-an-electric

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simonsarris
No it won't.

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...](http://wheels.blogs.nytimes.com/2010/10/21/mazda-next-generation-
mazda-2-will-get-70-m-p-g/)

------
Construct
With a compression ratio of 14:1, it will be interesting to see if this car
requires 91+ Octane (Premium Unleaded). Higher compression ratios are a great
way of squeezing more power out of the same amount of gasoline, but raising
the compression ratio also raises the risk of detonation.

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.

~~~
cullenking
It's guaranteed they are using some sort of variable valve timing, however I
wouldn't dismiss a non-timed 14:1 motor. If they toss in some forged internals
and keep the displacement small, they don't even need any sort of VVT to lower
the dynamic compression ratio. My R6 has something like a 13.1:1 compression
ratio with no VVT. Granted, the cam probably has some overlap.

~~~
Construct
Good point.

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.

------
cullenking
People still won't buy it unless it is decent sized and powerful. The same
reasons why VW didn't bring in the 1 liter turbo diesel that got something
like 100mpg. The fuel has been available since 2007, there just isn't much
market yet. Drive fuel prices sky high again and maybe...

~~~
elai
Then why do you see smart cars everywhere? They're millage isn't that much
better than a yaris! I would love to have a climate controlled aerodynamic
motorcycle (which is what he 1L car is) A ton of people would purchase the
car. Hell you can go from SF to NY on 13 gallons of gas with it. Hell you
could put 2 Jerry cans in the trunk and never have to stop at a gas station!
Most of the time when I'm driving, it's just one or two people plus a few bags
of groceries, it's a great second car for anybody who has to commute 1 or 2
hours every day and have a family pile into the sedan when you all want to go
together.

~~~
lsc
_I would love to have a climate controlled aerodynamic motorcycle (which is
what he 1L car is_

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.)

------
JofArnold
As I often say "My 7 year old Rover 25 diesel gets actual 50mpg with 115hp
(0-60 approx 9s)... And the wreck only cost me $1500 (£1000 in UK)".

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)

~~~
cullenking
Actually, the soot in diesel exhaust is much more carcinogenic than that of a
(well tuned) gas engine. There are various studies, one california based study
showed diesel soot was up to 70% of cancer for californians. Not saying that I
want to breath either, but i'd rather suck down a mouthful of gasoline engine
exhaust than diesel soot while on my morning bike commute.

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.

~~~
simonsarris
In the US, yes, but thats a US problem.

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.

~~~
cullenking
Actually, in the US it was 500ppm in 2007 (LSD), and by the end of 2010 it
will all be ULSD (15ppm sufur) for onroad vehicles. 2014 is when the
exemptions for some small offroad vehicles and the like are removed.
[http://en.wikipedia.org/wiki/Ultra-
low_sulfur_diesel#United_...](http://en.wikipedia.org/wiki/Ultra-
low_sulfur_diesel#United_States)

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.

