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QUESTION: We hear much about reducing greenhouse gas emissions from motor vehicles, but never anything about the most insidiously poisonous of all, carbon monoxide. Has there been any progress in reducing this emission?

CO is, of course, the result of inefficient combustion, when not enough oxygen is available to convert all the carbon in the fuel to carbon dioxide. Has there been any progress in improving the abysmal inefficiency of the internal combustion engine?

Stewart

ANSWER: There sure has! Compared with engines of only 25-30 years ago, for a given unit of displacement, today's internal combustion engine uses half as much fuel to generate twice as much power while producing 98 per cent fewer harmful emissions.

The most graphic example that comes to mind is the venerable Chevrolet V-8. The 350-cubic-inch engine in the 1975 Corvette produced 165 horsepower and you were lucky to squeeze out 15 miles per gallon (15.7 litres/100 km). The 2007 version has a 6.0-litre V-8, produces 400 horsepower and can cruise all day at legal limits returning 30 mpg (7.8 L/100 km).

The improvements in efficiency have been made possible through the use of cleaner fuels, strict controls of how much is introduced to the combustion process and treatment of the waste stream.

Today's elaborate electronic control modules and fuel injection systems result in careful control and measurement of the fuel/air mixture.

Higher compression ratios, carefully designed combustion chambers and minute control of ignition and valve operation, ensure maximum use of that mixture and, oxygen sensors and catalytic converters in the exhaust stream monitor and clean the spent gases.

The catalytic converter gets most of the credit with respect to carbon monoxide. CO is a colourless, odourless, tasteless and particularly harmful gas left over when carbon-based fuel is burned. The problem is particularly nasty during cold starts and at higher altitudes when the fuel/air mixture is richened - or when the engine is out of tune.

Catalytic converters, which convert carbon monoxide to less harmful carbon dioxide, were introduced in the mid-1970s. By the mid-1980s, when three-way converters came into use, they were able to remove 80 per cent of the carbon monoxide from the exhaust of vehicles.

With the addition of sophisticated computers, oxygen sensors and tougher emission standards, today's internal combustion engine emits 90 per cent less CO than the equivalent vehicle from the 1960s.

Today's three-way catalytic converters also reduce the emission of nitrogen oxides by converting them to nitrogen and oxygen and vastly reduce the oxidation of unburned hydrocarbons by changing them to carbon dioxide and water.

The exhaust gas of the internal combustion gasoline engine in a 2007 vehicle is often cleaner than the ambient air entering the intake system.

Speedometer readings

QUESTION: I live in a rural area about 80 km northwest of Toronto. The OPP in this area place unmanned radar speed detectors/displays on many of the area roads and often in 40 km/h limits outside schools.

When I approach one of these speed indicators I usually set the cruise to prevent going too fast, because kids are unpredictable and I would hate to be responsible for an injury. I notice that when I set the cruise at 45 km/h, the radar dispaly will indicate I am doing 40/41 km/h or about a 10 per cent error.

I assume the radar is accurate and that my speedometer is indicating faster than my actual speed.

This doesn't trouble me a great deal, but I wonder if this error is constant over the range of the speedometer. At 100 km/h, is it still 10 per cent out, which would mean 90 mm/h on Highway 400, which is a little antisocial even in the right-hand lane where I normally drive, or is it still 4 to 5 km/h out.

John

ANSWER: Most speedometers are optimistic to the tune of about 2-4 per cent to allow a margin on the safe side.

But there are other factors at work as well and they all result in a pretty uniform error.

The most common issue is one of tire diameter, which may vary depending on size, wear and pressure or any combination of them.

As the diameter of a tire changes, so does the vehicle speed for a given engine speed. If you have replaced the original-equipment tire with anything other than the exact same size, if the tire pressure is a few pounds off the suggested setting or even if the tread has worn significantly, there will be a greater degree of speedometer error. It doesn't take much to make a difference.

Another factor is that cruise control systems vary greatly in their efficiency - some will allow speeds to drop several km/h before making the necessary correction and then accelerating past the set point before disengaging.

How to reach us

Automotive journalist Richard Russell has run a driving school for 20 years, is a member of the Society of Automotive Engineers and has been a member of the Technology of the Year committee of the Automobile Journalists Association of Canada for 10 years.

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