Matt Evans, product engineer at Future Facilities, explains why thermal management is essential to the future success of electric cars.
The days of diesel-powered and petrol-fuelled cars are numbered. Numerous countries around the globe have announced their intention to implement a complete ban on the sale of vehicles using fossil fuels, with both the UK and France pledging to outlaw purchases by 2040.
It’s no exaggeration to say this represents the most seismic shift in the automotive industry this century. And as with any significant evolution, it brings along a great deal of excitement, but also a large number of challenges.
Engineers will be thrilled to experiment with the possibilities of lithium-ion battery powered cars – much like the vehicles Tesla and other manufacturers are already producing – on a larger scale moving forward.
But the tricky part will be how they stand-up to direct comparison with traditional internal combustion engine (ICE) powered cars. The absolute minimum requirement will be to match these legacy vehicles when it comes to variety, reliability, handling and that all-important intangible: driving experience.
That’s to say nothing of the peripherals that we’ve all become accustomed to — satnav, air-conditioning, heating and in-car entertainment to name but a few. Will electric cars be able to rise to the challenge of matching, or even surpassing, ICE vehicles in all these aspects?
It’s certainly not a journey that will be taken in cruise-control. Innovative solutions will be needed to ensure that electric cars are able to reach their full potential. And this is especially true when it comes to the thermal management of lithium-ion batteries and other vital components.
Thermal challenges
In traditional ICE powered vehicles, thermal management is primarily focused on removing heat from the engine, which unsurprisingly, runs fairly hot. Of course, reducing any possibility of the engine over-heating is crucial for reliability, but for the most part, the tolerances of operating temperatures for mechanical components are quite generous — particularly when compared to the components in all-electric vehicles.
Lithium-ion batteries must be kept within a strict, narrow window of operating temperature. Anything below 0°C and the chemical reactions within the battery will slow down, impacting performance and range. Go above 30°C and the battery begins to deteriorate exponentially — past 40°C irreversible damage will likely occur.
The optimal temperature range for these batteries tends to be between 20°C to 30°C, which may be easy to achieve in a vacuum. However, cars operate in areas where environmental temperatures have wide variability. In the UK alone — not particularly famed for wild swings in temperature — lows of 0°C and highs of 35°C are fairly common. So, even in quite temperate areas, some days the batteries will need to be warmed up, and on others cooled down below ambient.
Unfortunately for engineers, these are not the only challenges when it comes to thermal management of electric cars. Careful, precise management of the power electronics components is vital — otherwise ‘thermal runaway’ becomes a very real danger.
Simply put, this is a situation where increased ambient temperature changes the operation of the power electronics device, leading to a vicious cycle of further temperature rises. As the junction temperature elevates, the on-resistance of transistors increases, which in turn creates more heating of the junction. The end result is electronics burning out and components failing, which could be incredibly dangerous in automotive applications.
Another obstacle engineers must overcome lies with the electric motors used to power electric cars. Because of their axle-mounted position, cooling electric motors is a much more complex challenge than with traditional ICE vehicles, where the motor is located in the engine bay with plenty of opportunity to benefit from airflow emanating from the front of the car.
Success through simulation
Looking at the scope of the challenges the automotive industry faces as it transitions to producing electric vehicles at scale, it’s clear that thermal simulation will be absolutely critical to their success.
Prototypes are costly and time-consuming to produce, especially when you consider the large number of components that a product as complex as a car will contain. Thermal simulation provides a solution that allows engineers to extensively test a system in a full range of operating environments, identify any thermal issues, then design and optimise a solution in a matter of hours or days — as opposed to weeks, months or even years.
However, if simulation is not carried out in an extensive and intensive manner, manufacturers will simply face the same old problems. When it comes to designing electric vehicles, engineers need the tools that can perform a full, detailed, analysis.
In particular, engineers must be equipped with computational fluid dynamics (CFD) software that can import, handle and solve the complex geometries involved in automotive design, where electronics are designed to fit into the limited space available, often within curved body shells or dashboards. Unfortunately, this is something legacy thermal simulation tools too often struggle with.
Evolving technology
2040 might seem a long way off as we’ve just entered the 2020s, but the deadline will still loom large in the mind of car manufacturers. Especially given technology is constantly evolving, presenting new challenges in terms of thermal management. Many industry experts are already looking eagerly at the potential of solid-state batteries to replace lithium-ion and provide faster charging coupled with reduced weight.
With this shifting landscape in mind, the flexibility, reliability and accuracy of thermal simulation using CFD software for electric vehicles will prove a vital partner on the road to continued success for the automotive industry.