Pre-heating the Prius Transaxle and Engine for better fuel economy

[orange4boy]

I just identified an interesting thing from my junk box... a 240VAC 75A frewheeling diode SCR rectifier.

EFE01CFSE. Circuit 01 on the pdf.

http://www.galco.com/techdoc/crdm/ef_cp.pdf

I'm assuming the control leads turn it on and off. Is this the heart of a charger? Just need to get the voltage up a bit. How is that done? <scurries off to find electronics book>

[orange4boy]

Success! Stage 4, 70˚C engine coolant temperature, in the garage in 40 minutes.

And a record commute: 4.3 L/100Km (54.7 mpg) my old record was 4.8 (49 mpg) and my average without preheat was 5.8 (40.5 mpg)

KWH and costs TBD.

Percent better: 25

Approximate gas savings per tank (assuming all island driving): $10

Keeping my honey warm: Priceless.

And my very first graph. Even pricelesser.

[orange4boy]

Iv'e been getting a steady 4.3-4.4 L/100km on my commutes with both engine and trans preheat and 4.8 and above without heat.

Now I'm testing the mild plug in battery running the 12V side. Just got it hooked up and a record commute of 3.9 L/100

[2009Prius]

Originally Posted by orange4boy

...

And my very first graph. Even pricelesser.

Was this graph recorded with both the engine and the transaxle heaters running from time 0:00? If so then does this mean that the engine heater heats up the engine much quicker than the transaxle heater does the transaxle? Thanks!

[orange4boy]

Originally Posted by 2009Prius

Was this graph recorded with both the engine and the transaxle heaters running from time 0:00? If so then does this mean that the engine heater heats up the engine much quicker than the transaxle heater does the transaxle? Thanks!

Yes. The engine heats up much faster partly because it has a much smaller mass than the transaxle. The coolant temp sender is also immersed in coolant in the engine whereas the MG1 and MG2 probes are in the windings so they would heat up slower and this would lag the coolant temp.

[orange4boy]

More preheat propaganda:

Testing Plug-in Hybrid Vehicles (PHEV) over standardized and real world drive cycles has shown relatively large fuel consumption differences between ambient cold starts and hot starts. Losses on the order of 25-40% have been observed from ambient 20oC cold starts to optimal hot temperature urban drive cycle operation (Figure 1). This is especially critical for PHEVs, when long durations between engine operation result in reduced engine temperature. Testing under this project begins to quantify these temperature effects and identifies areas for future vehicle efficiency studies and improvements to PHEVs.

Argonne researchers have applied response surface methodology techniques for PHEV experimental test data to characterize the thermal effect on efficiency [Figure 2]. Combined with a technique for predicting the engine thermal state from its initial temperature, this unique methodology accurately predicts the fuel efficiency over a drive cycle from ambient cold starts to fully operational temperature. Current work focuses on
developing a displacement-independent engine model that will allow vehicle simulations to account for engine thermal efficiency effects. Analysis from this methodology led to the following conclusions:

Engine efficiency significantly increases with increasing engine temperature.

Projected optimal engine temperature is ~25% more efficient than a 22C ambient cold start.

The initial enrichment spike encountered during a cold start accounts for a ~3% fueling increase compared to a warm engine. Greater accumulated losses (~20%) follow this cold start enrichment until the engine reaches optimum temperature.

Between the range of 25°C to 60°C, each 5°C increase in initial engine temperature decreases fuel consumption by 3.2%~1.9%, respectively. This fuel usage reduces as temperature increases, ultimately reaching an asymptote.

For the experimental PHEV, ten minute soak times may result in ~5 degree
variations in temperature (dependent upon powertrain operating temperature).

Losses associated with the electric components, rolling losses, and transaxles are minimal relative to engine and transmission thermal losses.

[bwilson4web]

This past winter, I've observed a few warm-up tricks unique to our NHW11s:

• 30-40 seconds catalytic converter warm-up - during this brief time, gentle acceleration will clamp the fuel consumption at 0.60-0.70 gallons per hour regardless of speed. The NHW11 functions like an EV drawing as much power as a soft-foot can noodle out and often achieve ending speeds of 35+ mph (+56 km/hr) and an indicated MPG of 35-40 MPG (5.9 - 6.7 l/100 km). I suspect this is so the HC converter valve can remain closed at the expense of traction battery charge. Ignition is severely retarded.
• "N" during warm-up, 0.30 gallons/hr - every time it coasts in "N", fuel consumption will run at this low rate regardless of vehicle speed.
• "D" acceleration during warm-up, +1.50-2.50 gallons/hr - this needs to be minimized until the coolant reaches +60 C.

What I verified this past winter is this 'gentle warm-up' above 40 F (4 C) can keep my 10 mile (16 km) trip mileage in the 50 MPG range (4.7 l/100 km.) Anything less gentle and I'm looking at 40-45 MPG. But below 40 F, the block heater for 30-60 minutes became necessary for a 50 MPG result. I live in North Alabama which means afternoon temperatures below freezing is rare and I don't have a work, plug-in . . . but I know how to 'gentle warm-up.'

Personally, I want a Prius dock, a smart parking curb. But it has to anticipate my trip, a hard problem. It would be a lot easier if the car had a legitimate reason for being on ... say AC and waste heat for the house. Well we have a natural gas line to the house . . .

Bob Wilson

[Frank Lee]

Having seen and pondered the various attempts to preheat engines/transmissions and the pros and cons... I did some digging and came across this:

Engine Blankets & Battery Heaters - Powerblanket

Seems to me it could be a one-stop solution for not only simultaneously heating the engine and trans... but everything underhood!

... some heat for the battery, belts, hoses, belt-driven accessories, etc. would be nice too!

I'm tempted to get one...

[bwilson4web]

Originally Posted by Frank Lee

Having seen and pondered the various attempts to preheat engines/transmissions and the pros and cons... I did some digging and came across this:

Engine Blankets & Battery Heaters - Powerblanket

Seems to me it could be a one-stop solution for not only simultaneously heating the engine and trans... but everything underhood!

... some heat for the battery, belts, hoses, belt-driven accessories, etc. would be nice too!

I'm tempted to get one...

I always encourage experimentation but there is an efficiency challenge of heat transfer. The block heater is a small rod just under three inches and about 3/8 inch diameter that fits in a recessed hole so the 450-500 W all goes into the block.

I also used two JC Whitney pan heaters on the transaxle and at least half of the surface was in contact with the pan. But both pan heaters broke their electrical connection at the heating pad (lessons learned.) Too much vibration between the engine/transaxle and the body.

Now if the bottom of the engine compartment was enclosed and the pad were inside, it would likely work. That would also solve the vibration problem, hardening and breaking the copper conductors.

GOOD LUCK!
Bob Wilson

[orange4boy]

I'm finally going to be properly able to test this soon. First of all, I have to correct a plumbing issue I have. The original place I spliced the tank heater into turns out to send the hot coolant into the transaxle rad, so instead of heating that I was mostly heating the air. There was an increase in the transaxle temp as read by the scanner, so it was working, but not very efficiently. I will now set that up properly so most of the 750 watts will get where it's supposed to go.