Thermal Management Strategies in ICE and EV’s

Content:

Introduction
Why is it important to regulate thermals in vehicles?
Thermal Management in IC Engines
Thermal management in EV’s.
References

Introduction:

Environmental limits for automobiles are evolving, posing new issues, particularly for internal combustion engines. With the same level of engine performance and thermal comfort, the goal is to reduce pollutant emissions and fuel consumption (and thus CO2 emissions). It's crucial to remember that vehicles are frequently utilized for short distances, and engines are typically operated at low loads and speeds. As a result, they are frequently employed at temperatures below their optimum and in transient thermal conditions. The combustion process is inefficient (due to the cold cylinder walls), post-treatment devices are ineffective, fuel consumption is high, and the passenger compartment cannot be heated during the warm-up phase.

Then it's crucial to cut down on engine warm-up time, which boosts fuel consumption by 5–30%. Only a third of the fuel energy released by the combustion of the fuel combination is turned to useful work, according to research. The remaining fuel energy is ejected through the exhaust gases, or to the coolant or lubricant circuits. The distribution of these circuits varies depending on the situation. The operational point of the engine (rotational speed and load) as well as the engine state of heat. Convective and radiative heat exchanges are used types, and they work in various regions of the engine.

Why is it important to regulate thermals in vehicles?

It is general knowledge that automotive electronics have become increasingly complex, and that power consumption continues to rise. The rise of gasoline-electric hybrid cars in recent years has exacerbated cooling issues with electronics that handle enormous quantities of electricity.

Fig . 1 : PV graph for different thermodynamic processes in IC engine

A cycle governs the operation of a heat engine. Heat is converted to work in the first stage by expanding a heated gas in a cylinder. The piston and gas must be returned to their initial state for the following cycle in the second step. In order for the engine to produce a net output of work, it must use less work in stage 2 than it did in stage 1. After stage 1, the hot gas can simply be evacuated from the cylinder in a practical engine. Cooling the cylinder is another option. In either case, heat is transferred to the environment, making it easier to return the system to its initial state. In other words, without dumping heat or hot gas, it would take as much work to perform stage 2 as was obtained from stage 1.

On the other hand thermal management in electric vehicles allows for not just increased battery power and longevity, but also smaller electric engines. As a result, temperature is the most important parameter to control in a battery, necessitating the adoption of appropriate electrical and thermal insulation materials. Here's a rundown of the important points to consider when it comes to thermal management.

The Joule effect causes any electric current running in an electrical conductor to produce heat, according to Joule's law. As a result, the more powerful a battery cell is, the more heat it generates. When designing a battery, the key factor that restricts power increase is temperature. Sensors are installed during the design phase of batteries to detect hotspots and control the interior temperature. Temperature has a big impact on battery performance because the pace of electrochemical reactions at electrode/electrolyte interfaces tends to increase with heat. As a result, increasing the battery operating temperature does not imply a decrease in performance, but rather the reverse. High temperatures, on the other hand, accelerate the ageing of all of the materials that make up batteries. Depending on the technology employed, electric batteries all have a certain level of sensitivity to the risk of thermal runaway. Excessive temperature rise, especially in lithium-ion batteries, which are known to be unstable, might result in a fire or possibly an explosion.

Thermal Management in IC Engines:

A)Oil Cooling:

Fig. 2 : Outline of oil cooled engines

Fig. 3 : Oil cooled engine with air cooled Fig. 4 : Oil cooled engine without air cooled

Fins Fins

The oil-cooled engine with air-cooling fins is shown in Figure 3, while the oil-cooled engine without fins is shown in Figure 4. After passing through the oil cooler, the oil cools the circumference of the combustion chamber, a spark plug, and an exhaust port, then circles back to the oil pan and cools the cylinder bore. The channel area of the cooling pathway on the cylinder head must be decreased so that the oil flow velocity increases, improving cooling performance. Convective heat transmission occurs between the cylinder and the oil, as well as between the oil and the casing. The fins on the engine aid in further cooling by allowing convective heat transfer between the fins and the air.

B) Water Cooling:

Fig. 5 : Outline of Water cooling system

Fig. 6: Water cooled engine

The schematic representation of the water-cooled system is shown in Figure 5. To promote engine warming, the water-cooled system has a traditional construction in which the thermostat is situated in the coolant outlet of the cylinder head. A water-cooled engine is depicted in Figure 6. The operation of a water-cooled system is comparable to that of an oil-cooled system. Water performs the cooling role, and convective heat transfer occurs within the engine.

When the temperature isn't too hot, the water and oil cooled systems come in handy. As a result, they're mostly seen in two-wheeled automotive engines. Engine temperatures in four-wheeled and high performance two wheeled autos are comparatively high. As a result, a more capable cooling system is required. In all four wheelers and high performance two wheelers, radiators are employed to keep the engine cool.

C) Radiator System

Radiators are nothing but heat exchangers which are used in automobiles for cooling purposes. It is also used in some railway locomotives and stationary generating plants. Radiators are most commonly used in IC engine cooling. Enormous amount of heat is generated in the IC engines to prevent the engine from overheating the coolant is circulated continuously through the engine. The coolant receives heat through conduction and carries it away from the engine block. The coolant is further circulated through the radiator where air is blown on the coolant pipe lowering the temperature of coolant via convection. The radiator passes the coolant through thin metal fins making the heat transfer easier. The radiator fan blows the air across the radiator in order to remove the hot air from the engine bay. Radiator structure can be seen in the figure 7.

Fig. 7 : Radiator block of engine

Thermal Management in EV’s :

Given that electric vehicles are the future of automobiles in general, it is critical to appropriately regulate heat in order to improve the vehicle's efficiency and range. Li-Ion batteries are employed in the majority of sophisticated systems because they have various advantages, including increased range, reduced weight, and reduced battery area. Given the current state of technology, Li-Ion batteries are an ideal alternative for electric cars due to their high power density. The ideal working temperature of such a battery pack, which is between 15 and 30 degrees Celsius, is one of the criteria that come with it. The battery must have a thermal management mechanism, either passive or active, that ensures it stays within this temperature range at all times.

Thermal management of the batteries may be done in two ways. There are two types of management: active management and passive management. Passive systems are less expensive, easier to maintain, and use less energy, but they are difficult to manage precisely. On the other hand, active systems are those in which the cooling medium is actively circulated through the system. It is often feasible to keep the battery at the precise necessary temperature with an active system, but it adds to the total complexity and expense of the system. Active management system is shown in figure 8.

Fig. 8: Active cooling system in EV’s

Air cooling:

There are several advantages. Air cooling systems are similar to internal combustion engines in that they are inexpensive, simple, and light. The downsides, on the other hand, are as obvious. Air-cooled systems aren't extremely adaptable, lack precise control, and can only function within a limited temperature range. As a result, this method clearly comes within the category of battery passive temperature control.Figure 9 (a) and (b) represents the series and parallel air cooling systems respectively.

Fig. 9: Series and parallel cooling of battery pack

Liquid Cooling:

Fig. 10: Battery pack liquid heat exchanger structure

Liquid cooling is a type of active thermal management that has a number of distinct advantages. Liquid cooling, like internal combustion engines, allows for fine temperature control but has a number of drawbacks, including high complexity, weight, expense, and the need for external flow circuits and pumps. They also use the battery's energy output, lowering efficiency.

Water, glycol, oil, and acetone are common liquids used in cooling systems. Figure 10 shows a battery pack liquid heat exchanger system.However the size of radiator required in EV’s is comparatively smaller than that of IC engines due to lower heat produced in batteries.

References:

[1] Tanaka, Koichi; Arase, Kunio; Kitayama, Amane (2016). SAE Technical Paper Series [SAE International SAE/JSAE 2016 Small Engine Technology Conference & Exhibition - (NOV. 15, 2016)] SAE Technical Paper Series - Development of Oil-Cooled Engine for Optimization of Engine Cooling System.

[2] Kim, Jaewan; Oh, Jinwoo; Lee, Hoseong (2018). Review on Battery Thermal Management System for Electric Vehicles. Applied Thermal Engineering.

[3] Deng, Yuanwang; Feng, Changling; E, Jiaqiang; Zhu, Hao; Chen, Jingwei; Wen, Ming; Yin, Huichun (2018). Effects of different coolants and cooling strategies on the cooling performance of the power lithium ion battery system: A review. Applied Thermal Engineering.

[4] Daotong Chong;Maoguo Zhu;Quanbin Zhao;Weixiong Chen;Junjie Yan; (2021). A Review on Thermal Design of Liquid Droplet Radiator System . Journal of Thermal Science.

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Thermal Management Strategies in ICE and EV’s