Improvement of fuel efficiency in automotive Eunsik John Bae & Martin Agelin - Chaab

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, ON

Experiment Setup

Introduction

Road transport is a necessary part of our civilization but

it largely depends on fossil fuels which contributes to the

pollution of our environment, global warming and lack of

energy security. One way to reduce our dependence on

fossil fuels is the introduction of electric vehicles. How-

ever, these have limited driving range so effective ener-

gy budgeting is critical. Road vehicles experience aero-

dynamic drag force for which up to 50% of fuel is used

to overcome at highway speeds. Drag reduction is a

cost effective way to improve fuel efficiency in road vehi-

cles and is particularly important for electric vehicles.

Another issue with electric vehicles is overheating of the

battery. Therefore cost-effective cooling of the battery is

desirable. This research proposes an integrated passive

approach to these problems. The objective is to design

and study the use of a rear diffuser for both drag reduc-

tion and electric battery cooling for an electric vehicle.

This is done using computational fluid dynamics (CFD).

Another way to reduce our dependence on fossil fuels in

vehicles is the use of low carbon blended fuels. This

project has built a test rig to test the utilization of various

blended fuels including hydrogen, natural gas, ammonia,

etc.

From the research paper, “Experimental study of multi-ple-channel automotive underbody diffusers” by L Jowsey and M Passmore, the best angle for the under-body diffuser was from 13° to 16° with four fins attached to square block model. The model used was designed to be more aerodynamic then the model used in the re-search paper. This would give us the practical data needed. The wind speed is set at 27.8 m/s for overall experiment. The pressure data is to be collected to de-duce the relative drag magnitude.

Figure 1. Body mesh of the model car (2mm mesh)

Figure 2. Body mesh of the model car in 3D view

Diffuser

To find which angle is best suitable for the model car

diffuser, pressure data has been collected from the

CFD. Diffusers were installed in a way to keep the bot-

tom of the car flat and smooth.

Figure 3.

Model of Diffuser

with 13 degree an-

gle.

(Upside down)

Figure 4. Point of

the pressure meas-

ured on the top of

the model car. (does not include diffuser)

Figure 5. Top

pressure data from

Different Diffuser

Angles.

Figure 6. Detailed

view for the rear

end of Top pressure

data from Different

Diffuser Angles

Figure 7. Points of

the pressure meas-

ured at the bottom

of the model car. (does not include diffuser)

Figure 8. Bottom

pressure data from

Different Diffuser

Angles.

Figure 9. Detailed

view for the rear

end of Bottom pres-

sure data from Dif-

ferent Diffuser An-

gles.

The diffuser models significantly reduced the drag at

the rear ends compared to non-diffuser model

From different angles of approach, the 13 degree

angled diffuser had most efficient drag relative to the

14,15, 16 degrees.

Results

Passive Cooling

A major issue with the electric vehicles is overheating the

battery. This requires cooling a system to be built in the

car, which adds extra weight, and consumes power that

decreases the driving range. The alternative way to solve

this problem is to introduce the passive cooling for the

electric vehicle.

The model for passive cooling concept being used, comes

from Tesla’s battery pack design. Which allows for more

surface area contact with the air at the bottom of the car.

Four different passive cooling design including two modu-

lar, and two fixed.

Modular designs were considered because they required

less assembly, are more cost friendly and allow for more

air circulation.

Fixed designs were also considered because they produce

more heat transfer, steady laminar air flow but cost more

than modular designs.

All fin models were considered as Aluminum 2014.

Test were done with the battery temperature at 360K, and

wind speed of 27.8m/s.

Figure 10. Layout

and temperature with-

out the passive cool-

ing fins.

Figure 11. Modular models for Passive Cooling

(Air flows from Top to Bottom)

Left: 5 evenly distributed Fins for top and middle

Figure 12. Fixed models for Passive Cooling

(Air flows from Top to Bottom)

Left: Center fins without side cooling fins.

Right: Center fins with side cooling fins.

Passive cooling with Diffuser

From the result of Diffuser and Passive Cooling, the two

most effective models were considered and joined to deter-

mine whether they will also decrease the drag of the vehi-

cle.

Figure 13. Comparison of the bottom pressure with three

different models.

Results

· From the figure 13, it can be seen that having more fins

combined with the passive cooling concept and the 13

degree diffuser can increase base pressure. This indi-

cates the passive cooling concept and the diffuser works

better when the two are combined.

The passive cooling has the fins which it allows steady controlled flow (where the pressure is higher) compare to non cooling at the bottom.

Conclusion

Alternative Blended Fuel Low carbon fuels were considered due to their low

carbon emission .

As an alternative blended fuel, hydrogen enriched nat-

ural gas and other low carbon fuels can be used for

existing road vehicles.

The testing unit was designed to allow for mixing of

various gases and liquids in a quick and easy manner.

Flowmeters control the blended fuel ratio. Flame quali-

ty and combustion efficiency will be measured and an-

alyzed.

Figure 14. Test rig setup

Next step

Angular diffuser design is to be considered.

Alternative passive cooling concept will be considered with different

battery model such as Chevy Volts.

Wind tunnel testing is need to be conducted with design models.

Due to safety factor, both ammonia and hydrogen gas needs safety

cabinet. .

Setup the fume hood to collect any gases during the operation.

Alternative piping might needed to prevent corrosion.

Figure 15. Schematic for test rig cycle

13 degree angle diffuser with most fins

from figure 12 works best on both drag

and cooling.

Passive cooling and diffuser helps

steady flow to the underbody.