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Old 05-18-2020, 10:15 AM   #8
arghx7
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Quote:
Originally Posted by vapore0n View Post
So MPG goes down then?
I thought the whole move to smaller engines was due to the MPG requirements.
The MPG requirements are determined on test cycles that have very mild driving, or the aggressive driving portion is only a small portion of the final calculation. It applies for both Euro and US cycles. There's a realistic (heavy acceleration to highway speeds) portion but much more of the testing is based on stop and go city type traffic.

So when you drive in the real world and hook up portable emission measurement equipment, the emissions that occur under boost/heavy loaded driving spike. That's CO and particulate in gasoline direct injection and NOx/particulate in diesel. To fix that you basically need a bigger engine that doesn't work so hard, which is then carrying around the extra weight and friction in lighter loaded driving.

Then it just becomes easier to spend money on electric motors and batteries as full BEV or strong hybrids, or play regulatory games for regulatory credit (add some device and do paperwork to demonstrate the CO2 benefit in the real world).

There's always been a tradeoff between tailpipe air quality emissions and fuel consumption/CO2. Back in the 70s they tightened up tailpipe air quality emissions faster than fuel economy/CO2 type regulations. So they had these emission systems called thermal reactors instead of cats. With that system the car drove around running rich all the time with retarded spark, then pumped air into the exhaust manifolds to burn it up. Fuel economy was terrible but tailpipe emissions were clean by the standards of the day. 70s Porsches and 70s Mazda rotary engines used that type of system for example.
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Last edited by arghx7; 05-18-2020 at 10:21 AM.
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