Quote:
Originally Posted by Sven7
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I've been looking around for stats on pre-warmup emissions on gas engines but can't find any numbers. (Trying to justify a block heater to someone on the local forum). So, how much less efficient are they when cold? Are they only inefficient during those five seconds of high idle at startup, or do they chug more gas until the temp is up?
Edit
The big question is this: Which emits fewer greenhouse gases: 800Wh of coal-fired electricity or the amount of extra gas your cold engine burns?
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MetroMPG included some stats on his page:
In praise of the lowly block heater - MetroMPG.com
I haven't done the comparison vs the grid, but I agree that's a key point. (Still pretty sure the block heater is favored, just thinking back of the envelope - % smog blamed on coal vs gasoline.)
The effectiveness of the block heater is not all about the cat though. Cat light-off temperature (50% efficacy) is like 300°C, so pre-warming the engine doesn't shorten cat light-off a ton. I'd bet the effect of the block heater is equally for fuel vaporization and cold-idle speed. (See section 1.2.3 in "Modelling and Control of Automotive Coldstart Hydrocarbon Emissions".)
This should give you an idea how a cat behaves vs temperature:
Unfortunately this chart is just a model, not real data.