CFD Simulations Can Reduce Automotive Emissions

(Image courtesy of Mentor Graphics.)

Computational fluid dynamics (CFD) simulations are fundamental tools that can help to make automobiles greener by reducing emissions and increasing fuel mileage.

Contemporary cars are complicated feats of engineering. They include many subsystems, so optimizing them for reduced emissions is a complicated task.

As a result, engineers will want to bring these CFD simulations into their design cycle as soon as possible. One way to do this is to use simulation tools that are optimized for designers, such as Mentor Graphics FloEFD which brings CFD into CAD tools like CATIA, NX, Creo and Pro/ENGINEER.

“The earlier you can add simulation into the design cycle the more time you have to optimize the whole device,” explained Boris Marovic, industry manager at Mentor Graphics. “You have a few months for your design cycle to get from the first ideas to the final product. If you run the simulation very late you might have one to two trials. If you do it early, you have more trials and are able to implement improvements faster and more often.”

But where should an engineer look to optimize the emissions of their vehicles?

Aerodynamics are Still Important to Reduce Car Emissions

The obvious place to look to reduce automotive emissions with CFD is aerodynamics. The smoother your car moves through the air, the less drag and resistance it will experience. As a result, less fuel is needed to maintain constant speeds or accelerate through air.

Aerodynamics are a great way to improve fuel efficacy and reduce emissions, but it’s not the only way CFD can make your designs greener. (Image courtesy of Mentor Graphics.)

To find the right mix of drag and lift on your car, engineers typically look to wind tunnels and CFD simulation. Areas of the vehicle like the side mirrors which are away from the car increase turbulence and resistance on the vehicle.

“Anything you can do to make the car drive smoother through the air with less turbulence to pull the car back will improve emissions,” said Marovic. “These obstacles increase the drag and create low pressure areas. The smoother and flatter the obstacles are, the more aerodynamic they are and the less fuel is needed reducing emission.”

However, external simulations can take a long time depending on the size of the model you are looking at. For instance, Mentor reports that a customer performed an external aerodynamics simulation with a meshing time of 15 minutes and a solution time of 18 hours for a model with 13.5 million cells.

So where else can an engineer look to reduce emissions? Marovic suggests that, “everything that reduces the amount of energy to propel a car, cool the electronics or to push a fluid through a duct can reduce emissions. This can be aerodynamics, but any device that is made more efficient or uses less energy to cool, smaller fans, better air-conditioning ducts all can reduce fuel consumption and emissions.”

Therefore, to have more chances of optimization, engineers might want to spend time on other systems or look at the aerodynamics of part of the car’s exterior such as mirrors, door handle or fenders.

How CFD Can Optimize Internal Flow for Reduced Emissions

Volkswagen flow straightener reduces the turbulence of the air flow for a more accurate fuel mix, which reduces emissions. (Image courtesy of Volkswagen.)

“If the engine is more efficient or works in the right temperature range, then emissions reduce,” explained Marovic. “This is also true when you look into the internal flow of the gases in the engine and how much turbulence there is when you spray the fuel to ensure good combustion. CFD can help with these calculations.”

Engines and internal flows are much easier to simulate than a car’s external aerodynamics since, for the most part, they consist of cylinders and ducts. As incomplete combustion increases the fuel emissions CFD can help.

Additionally, since all the cylinders in an engine are identical, engineers can optimize a lot of the car with a small amount of computing time. To simulate the flow into a cylinder of an engine, Mentor’s FloEFD will require less than five minutes to mesh the model and one to two hours to produce the results.

Engineers can also optimize the flow of air through the automobile HVAC system to reduce the size and power of the fan.

In fact, internal flow simulations like this are likely what engineers at Volkswagen used to improve their emission woes with their flow straightener. The device uses a mesh to reduce the turbulence of the air flow, producing a more accurate flow reading. This reading can then be used by the engine control unit for a more accurate calculation of the fuel mix needed to optimize the combustion.

Setting up the CFD simulation of an exhaust manifold. (Image courtesy of Mentor Graphics.)

However, internal flow simulations can do a lot more to reduce emissions by reducing fuel consumption. For instance, by improving the exhaust’s contact with the catalyst in the exhaust manifold, CFD can optimize the flow onto the catalyst for a better chemical reactions that reduces emissions.

Otherwise, if the exhaust is too concentrated in one area of the catalyst or if the flow is too fast then there may not be enough time for the chemical reactions to take place.

Where CFD Can Look in Your Automotive Electricals to Reduce Fuel Consumption

By using electronics with reduced power consumption your car will need less power to operate them and smaller fans to cool them. Both of these will translate into less fuel consumption.

Electronics cooling simulation comparison between FloEFD (top) and FloTHERM XT. (Image courtesy of Mentor Graphics.)

Though intuitively this might sound like small savings they can add up over time. This is especially true with electronics that produce a lot of heat like headlights, infotainment systems or the power electronics in hybrid vehicles. Therefore, using CFD to size the cooling systems is an important emissions saver.

To perform detailed electro-thermal simulations, you might need to use tools like Flotherm XT which can read in electronic CAD (ECAD) data as well as mechanical CAD (MCAD) data. This way the printed circuit board (PCB) designs and power distributions as well as the housing or cooling unit can be imported into your simulation.

However, for design engineers looking to perform simplified simulations early in the design cycle you can get away with more general purpose simulations. Perhaps all you need at your stage is a block with a heat source or a thermal compact model to estimate the thermal properties?

Running these simulations will take a little longer than your internal flow simulations so schedule wisely. For instance, Marovic explained that a headlight simulation took about 15 minutes to mesh and 8 to 10 hours to solve.

Marovic said, “The solution time will depend on how detailed the physics will be. If it is just heat convection and conduction, then the solver will perform much faster than if you have complex radiation or condensation in the simulation.”

Clearly aerodynamics of a vehicle isn’t the only source of energy and emissions savings that CFD optimizations can provide. What examples can you think of that we missed? Comment below.

For more on Mentor Graphics’ FloEFD and Flotherm XT click this link.

Mentor Graphics has sponsored this post. They have no editorial input to this post. All opinions are mine. —Shawn Wasserman