New and Improved NREL Automotive Simulator Predicts Drivetrain Efficiency

NREL has an easy-to-download tool that helps engineers and vehicle researchers investigate powertrain options.

One of the keys to effective design is good simulation. The ability to try dozens of possibilities, asking “what if” with a computer instead of nuts and bolts, pays off big. But validated simulation programs often don’t exist or can cost many thousands of dollars. That’s why a recent announcement by the National Renewable Energy Laboratory (NREL) is important to anyone who needs to estimate the impact of new technologies on light, medium, and heavy-duty vehicles.

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NREL's FASTSim program can calculate powertrain efficiencies for light, medium, and heavy-duty vehicles. (Image source: NREL)


The program is called the Future Automotive Systems Technology Simulator, or FASTSim. It is available here for a free download as either a Microsoft Excel or Python program. The program provides a simple way to compare vehicle powertrains, including conventional internal combustion engines (ICE), hybrids, battery electrics, and fuel cell vehicles. Efficiency, cost, performance, battery life, and CO2 emissions are provided in a series of tables and graphs.

The FASTSim program comes preloaded with a variety of vehicles and drive cycles. This includes the standard US, European, and Japanese drive cycles. There are options to modify the standard set of vehicles, or to upload custom designs and cycles. Using the simulation tool, it is possible to evaluate vehicle performance to quantify energy consumption differences among vehicle and powertrain configurations, determining how this consumption changes under different driving and environmental conditions.


The program developed from a previous powertrain research tool. “Before FASTSim was created, we had a vehicle powertrain model called 'Advisor' that had a lot of detail,” NREL Senior Research Engineer Aaron Brooker told Design News. “But we wanted to do something that didn’t require as much data all the time. For that model, we had an engine map with torque, speed, and efficiency. You had these curves, these contours, and looked up efficiency for an engine map. You had to have an engine map for that to work and you had to have an electric motor map, and that was torque and speed, and efficiency contours again, or electricity consumption contours. There was a lot of data that went into that. There were a lot of challenges that were easy to mess up and not do things quite right and get unexpected trends,” explained Brooker, who was the lead author of an SAE paper describing FASTSim.

The need was for a program that didn’t require as much initial input data. “We looked at what we could do to really simplify this. We found that you really could simplify down to a power versus efficiency curve,” said Brooker. “That made the controls and the details in the model a lot easier to deal with and made it more of an intuitive tool. Now, we have something that is a lot easier to use. It is easier to find data. For most vehicle options, you can find whatever you need online. You don’t have to do tests on an engine dynamometer—you can find most of the data online, put it in, and it works really well.”

NREL validated its new model with around 700 vehicles and matched within about 5% for fuel economy for most of them, according to Brooker.

Although a new version of FASTSim has been released, the basic program has been available for quite a while. “We’ve been working on it for more than ten years, from the first creation to where it stands now,” explained Brooker. The new release adds updated vehicle models—up to 2016 models. It has also been updated with engine maps to better match today’s vehicles.

Two Versions

The two versions of FASTSim have slightly different capabilities, explained Brooker. “The Python version allows you to do real world drive cycles and we have a database of real-world drive GPS cycles. Our Python version lets us run really long drive cycles, so we can cover a lot of real world driving and get an estimate of how different powertrains or different ambient effects for a given region might impact efficiency,” he said. “The Excel version is more focused on EPA (mileage) estimates—duplicating and simulating their dynamometer tests. You can also import your own custom drive cycles into the Excel version if they are short, say less than 20 minutes,” he added.

FASTSim has been used for many powertrain comparisons internal to NREL. The program allows gasoline, diesel, and natural gas internal combustion engines, hybrid electrics, full battery electrics, and fuel cell powered vehicles. Vehicle price, fuel cost, and battery life estimates allow comparisons of the different vehicle powertrain types, all at the same time.

The program has found users outside of NREL as well. “Externally, it’s a good scoping tool for whoever is interested in looking at what future powertrains might come online. Where it is really adept is when we put in future component targets, and this is a good level for that. We have used it for DOE goals on where we need to get to on component improvements in order to get the emission of energy improvements that we want to see,” said Brooker.

Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.

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