hybrid plateau
 

Hi,

Recently, I had occasion to analyze the EPA data for low mileage hybrids:
http://hiwaay.net/~bzwilson/prius/EPA_survey_010.jpg

What struck me was how commercial hybrids had plateaued between 45-50 MPG. Understand, I'm not out for individual performance but rather a more difficult challenge:

• What 'affordable' mods could add +5 MPG to stock hybrids?

Think in terms of "JC Whitney" mods, something that doesn't take our skill level to install. I'm sniffin' around for what is often called 'low hanging fruit.'

My short list:

• full block, bumper inlet block - using an under body or other vent. The idea is a unit that either handles damage easily and/or is cheap enough to be replaces for little or no cost.
• rear wheel covers - a simple system that can be easily painted and removed or flipped to handle tire rotation or repair.
• Prius docking station - a curb that the owner parks on that handles engine compartment, not just engine or transmission, pre-warmup. Ideally it works out doors.

Thoughts?

Bob Wilson

A full belly pan and block heater would be easy and cheap mods.

The cooling air path won't benefit by being convoluted. I'd focus on making smooth, sealed ducting to the rad that can flex to vary the intake area to meet demand. I'd try to center the intake at the front stagnation point to minimize fan use.

I wonder if we might benefit from using oversize rads to reduce the needed airflow. I guess it wouldn't be hard to put a thermometer probe on each side of the rad to compare outflow temperature to water temperature in the top hose. There are probably aero benefits to slower flow through the rad as well as reduced volume. The team that built the globe-circling Voyager aircraft had to write their own textbook for our kind of speeds, and still gave up 20% of total drag to cooling - while flying, not rolling. I smell fruit.

I've often wondered why a cooling system needs a radiator. Why not just a long aluminum pipe running fore and aft that uses the air running under the car to cool the antifreeze passively? My bone stock Maxima barely gets to 190 degrees on a 90 degree day (while driving conservatively mind you) and I suspect allowing it to get to 210 wouldn't hurt anything.

Why does a cooling system have to be non aerodynamic? Often questioning common logic gets me in trouble, so dish it out, no need to be nice :D

I've often envisioned a shallow aluminium tank under the car full of antifreeze ready to cool to replace the mileage sucking radiator as we know it. Some insulation between the body and pan would keep heat out of the car quite nicely I imagine, but I don't know everything

Radiators have evolved to maximize the area for heat transfer with minimum weight and cost. A few ships have used the type of pipe you describe, but they are transferring to water. The 1911 Napier had its engine surrounded by copper pipes to make a streamlined enclosure with cooling surface. Generally, you want to protect the pressurized coolant from casual damage.

Theoretically, a duct with a rad can work as a low-temperature jet engine and add thrust. Many texts refer to the P-51 Mustang aircraft achieving negative drag from the rad housing, but it wasn't copied on the Voyager. As is usual on aircraft, it had a variable exit, rather than a variable intake, but that made little difference to the air. With the flow restricted, the ring of stagnant air replacing the stagnation point would just reduce its diameter, while the high pressure zone handled the flow shaping adequately.

A snowmobile has a underbody panel system like the one you describe, but if it is not sprayed with snow, as when running on ice or roads, it overheats.

This could be amazing! A belly pan and no radiator. :thumbup:

But remember you have to design for worst case. I bet the temps you see are driving on fairly level roads. You'll generate a lot more heat when you're e.g. climbing 4000 vertical ft at a 6% or steeper grade.

This winter I fully blocked our ZVW30 (2010 Prius) bumper air inlet and saw a 5% improvement in mileage. I'm thinking a bumper air inlet block with a valve wired with the fans or thermistor might be an answer. The trick is curving the valve edges so we don't get whistles and air noise.

The other challenge is handling bumper events. It needs to deal with minor incidents and in the event of damage, be repaired or replaced for little money. This makes the problem much more interesting.

Bob Wilson

Interesting picture. Assuming they are all stock, the main variable is the nut behind the wheel.

There's a lot of people in the middle who drive "normally"

Theres some leadfoots on the left.

Theres some extra efficient drivers on the right.

Would look different if it were L/100km.

What is the unlabeled x-axis of that graph?