How warm-up affects FE

It is really hard to watch the low FE readout on my Scan Gauge during warm up (15-18 mpg, the horror!). But at least during my 16 mile commute I make it up.

 

My approach is to get things ready in the morning, iPod, seat belt, e.t.c., and start the car. Without being heavy on the accelerator as soon as it is "READY," I pull on to the neighborhood street, accelerate to ~25 mph, and shift into "N" at every opportunity. The goal is to let the engine run in "N" as much as possible to minimize battery charging or extra load while rolling down the street. Once the engine auto-stops at a light or stop sign, I drive it normally.

This is the same technique I use with my NHW11 commuting car except I have travel about 1.5-2 miles (2-3 km) in this mode. The ZVW30 is ready to go in just over 0.5 mile (~1 km).

Bob Wilson

 

Bob,

Can you explain the reasoning behind this (the highlighted text), please?

 

One of the big differences you are experiencing is that the engine will not go into catalytic warmup while it is in neutral (true to its nature, neutral is as "safe-mode" as you can get) but it will continue to warm up to operating temperatures. The gas savings you are seeing are likely the result of canceling catalytic warmup thereby increasing emissions...saves on gas yes, but not on emissions because the catalytic converter is not being properly warmed before use.

This behavior is true for all generation Prius models.

Andrew

 

For those curious about my ZVW30 protocol, my experience has been:

• ~25 MPG - if I keep it in "D" to first auto-stop
• ~30+ MPG - if I maximize "N" to first auto-stop

In my case, the first stop light is ~0.5 mile (~1 km) from the house. All I can do is suggest replicate the protocol and post the results.

Now I understand it would be ideal if I had an exhaust, gas analyzer to measure the actual emissions. All I can do is report what data I've been able to capture from my NHW11 (the ZVW30 data won't be available until the fall.) My observations are:

• warm-up rate is not significantly faster in "D" vs "N"
• fuel consumption is 25-50% higher in "D" vs "N"

I have the ability to monitor mass flow (aka., fuel consumption) and ICE coolant with the ZVW30. I'll take some time to make the measurements but it will take a couple of days. Fortunately, we've had a cold front come through so the data should be pretty good.

Bob Wilson

 

Thanks, Bob.

 

I wrestle with the same warm-up problem when going to lunch from work. The trip is only about a mile, but it kills my FE for the day because the engine is on most of the way. Even if I let up on the gas pedal, the engine won't turn off since it's in warm up mode. However, I've found that if I stop for 5 seconds or so, the engine will turn off and I can then proceed in electric-only mode. The path to lunch is through low-traffic parking lots and side streets on flat terrain so I don't have to go fast enough to trigger the ICE again. So I can pulse a bit with battery and then glide for a while. I know that I'm using a bit of battery that will need to be repaid next time I start my commute (on the interstate) but it seems like a reasonable tradeoff to keep the engine off at lunch.

I could probably just start up in EV mode and accomplish the same thing, but thought I'd pass this along.