With each new euronorm (European emission standards) the restrictions are more difficult to comply with. Manufacturers solve this by increase the engine’s CC and make it consume more fuel. How does this result in being a “cleaner” engine, burning more fuel sounds contradicting to me.
example, motorcycle triumph:
Old model: Tiger 800 – 799cc – 95HP – consumption 4.7L/100km – EURO 4
New model: Tiger 900 – 888cc – 95HP – consumption 5.2L/100km – EURO 5
In: Engineering
I do not know this for sure, but my best guess is that they put roughly the same amount of fuel into a larger engine so that the engine produces the same emisions as a smaller engine. This will give the appearance of being cleaner. It’s also possible that they do some extra tricks with things like EGR systems and variable timing that actually do lower the power of the engine at full throttle, but wind up being more efficient for daily driving. Much like in the 70’s where all of a sudden a chevy v8 put out a whole 150 hp, the only choice they have is to “tune down” engines to pass because they simply don’t know how to do it any other way. The good news is that on engines that they do this to, there is a much greater chance for power gains in the aftermarket. Like the 5.0 engine in the fox body mustangs. Lots of room for improvement.
CO2 emissions are determined by how much fuel you burn, and if an engine burns more fuel, it puts out more CO2.
However, other harmful emissions (HC, CO, NOx) depend on how clean the burn is. In order to burn the fuel cleanly, the engine needs to mix air and fuel at exactly the right ratio. If there’s too much fuel and too little air, you have unburnt (HC) or partially burnt (CO) fuel coming out of the tail pipe. If there’s too much air and not enough fuel, some of the excess oxygen will react with the nitrogen in the air to create NOx.
An engine that runs lean (with too much air and too little fuel) will consume less fuel, but it will produce a lot of NOx. Adding more fuel will increase the amount of CO2 but decrease the amount of NOx. So sometimes burning more fuel can result in a cleaner burn.
Then there’s the catalytic converter. Pushing the exhaust through a catalytic converter will make the engine work harder, reduce its output power by a bit and require a bit more fuel. But the advantage is that a catalytic converter can take the oxygen atoms from NOx molecules and give it to the CO molecules, so harmful NOx and CO gets turned into relatively harmless N and CO2. Again, you give up some power and fuel efficiency to reduce harmful pollutants.
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