Hi all, A member of Prius-PT.com has recently noted the differences in emissions between the 2nd generation and the new generation Prius. This sums it all: +------------+----------+----------+---------+ | | Prius 2G | Prius 3G | Delta | | |----------+----------+---------+ | Euro class | Euro IV | Euro V | N/A | +------------+----------+----------+---------+ | CO2 (g/km) | 104 | 89 | -14.4% | +------------+----------+----------+---------+ | CO (g/km) | 0.18 | 0.258 | +43.3% | +------------+----------+----------+---------+ | HC (g/km) | 0.02 | 0.0583 | +191.5% | +------------+----------+----------+---------+ | NOx (g/km) | 0.01 | 0.0058 | -42% | +------------+----------+----------+---------+ The question, you guessed it, is why on earth do we almost triple the HC emissions and also have an increase on CO. To the best of my knowledge, which is quite limited here and hence my request for assistance, the HC is unburned fuel, and CO comes from insufficiently (badly) oxidized fuel. IF this is true, and note the big "IF", this means the 3rd generation is not burning all the fuel down, and that contradicts its bigger efficiency and puzzles everybody. Is anyone capable of explaining why this happens?
We know 3G has no bladder. There should still be a carbon canister to capture evaporative emissions, but presumably using just a canister doesn't achieve the same results (otherwise there would never have been a bladder to begin with). But still, a 200% increase seems unusual. ETA - I have no idea if the Euro standards take evap into account. I assume they do.
I don't think so, but I'm open for debate. In my mind the fact that we have a larger ice does not mean it should not burn the gasoline completely. All of Toyota's tech promotion on the 3rd Gen mentioned the lambda=1 fact (perfect combustion, no superfluous oxygen, no superfluous gas), so this is shocking news to me. Also, the fact that CO2 and NOx is lower, proves that the larger ICE has little to do with emissions, or at least it seems to. This is a big mystery to me.
The European version (and all others except USA one) had no bladder. The carbon canister is there since the beginning, my 2006 has it, no changes there AFAIK. Yeah, the 200% increase is a BIG one, that's what I think too, very strange indeed.
Very interesting, the increase in HC. I'll be curious to find out the reasons. However, if I am reading the graph below correctly, OP's reported numbers are errant, since we know the G3 Prius meets SULEV requirements, but the HCHO limit is 0.0024 grams/km. As for OP's question how the mpg can be better while unspent fuel is higher, that is easy: 1.15x of 99.7 is a lot more than x of 99.9, where 'x' is the thermo efficiency of G2 engine, and the 99 numbers, the fraction of fuel utilized. In fact, rather close to 15% better Or put another way, the G3 engine wastes 0.23%* more fuel than the G2 engine. This pales in comparison to the G3's engine efficiency improvement of around 15% in Euro testing. *((1 - 99.7/99.9)(104/89))*100
It's simple - the G2 is tuned more for emissions, the G3 is tuned more for fuel economy for this particular test. With the engine running less, burning less fuel, it's temperatures are going to be lower, leading to higher levels of HC and CO emissions. The same reason the G2 turns it's engine on after startup whether you're going anywhere or not and the first 5-10 minutes of fuel economy sucks - by making sure the engine and catalytic converters are up to proper operating temps, HC and CO emissions will be lower, even though you may burn more fuel. The same reason CARB makes high volume PHEV conversions go through the same forced engine warm-up cycle - even though you may never intend to run the engine for more than 30 seconds for your whole trip. Also keep in mind that the numbers only represent emissions for those particular test conditions. There are likely other situations where the G3 exceeds the emissions of the G2.
You're talking about a different unit (grams per mile), on a different test procedure. EU and US numbers are not directly comparable. I think there may have been a change to the test procedures between Euro IV and Euro V (not least, that emissions are now quoted in mg/km rather than g/km). Taking the Volvo S40 T5 6-speed manual, you see the following changes: Model Year 08: CO2: 208g/km CO: 0.088g/km HC: 0.023g/km NOx: 0.014g/km Model Year 10: CO2: 203g/km (-2.4%) CO: 0.256g/km (+190.9%) HC: 0.044g/km (+91.3%) NOx: 0.019g/km (+35.7%) Other vehicles are similarly affected. Handily, BMW seem to have recertified their 123d with DPF in March: Euro 4: CO2: 138g/km CO: 0.405g/km HC: - NOx: 0.178g/km HC+NOx: 0.231g/km PM: 0.000g/km Euro 5: CO2: 138g/km (no change) CO: 0.1408g/km (-65.2%) HC: - NOx: 0.1364g/km (-23.4%) HC+NOx: 0.1808g/km (-21.7%) PM: 1.210mg/km Despite changes in the individual pollutants from which fuel consumption is back-calculated, the stated fuel economy results are the same. If I were to guess, I'd say that the emissions measurement was changed from the full combined cycle to just the cold start urban part. Hence, you get more CO+HC emissions (which tend to happen on a colder engine) and less NOx (which, on a petrol engine, are formed when the engine is hot). I can't find a reference, though. There's probably a regulation somewhere on europa.eu but I can't find the right document. In terms of fuel consumption, note that the new Prius fuel consumption figure stated is 3.9L/100km, or 0.039L/km. Fuel weighs about 0.71-0.77kg/L, so it gets through about 27.7 grams of fuel in 1km. The HC emission figure represents about 0.2% of the fuel going unburnt. (This is why claims to improve fuel economy by improving the burn are such nonsense.) Similarly, compare the CO emission (incomplete burning) to the CO2 emission (complete burning). It's about 0.29%. The key indicator for the fuel economy is the huge drop in CO2 emissions. The rest is virtually just noise.
Nice catch - that likely explains all the differences, not the Toyota engineers working to extract more energy out of the engine at the expense of emissions. Can anyone verify? You explanation makes perfect sense.
Mike Dimmick, Your guess that emissions are now tested during a cold engine certainly fits. As for your other comments: I corrected for mile/km, so that is not it. I also doubt the gram->mg answer, since the results are nowhere near a 1:1000 difference. I agree about the emissions; you explained it clearer than I did. Cheers
