1. Introduction
In recent years, electric vehicles (EVs) have gradually become the main force in the automobile market due to the introduction of emission regulations of traditional fuel vehicles. The safety of the Li-ion battery under abusive conditions is still a technical barrier for electric vehicles [
1,
2]. Dendrite growth and overcharging can lead to particularly catastrophic thermal failure due to high rates of heat generation [
3]. In actual situations, local high temperature can also cause a short circuit inside the battery, further increasing the temperature and increasing the risk of thermal runaway [
4].
In regard to EVs with a lithium-ion battery pack as the main power, the performance of the battery pack mainly depends on the temperature difference between cells [
5]. Overheating of the battery may adversely affect the operation, durability, and life of the battery components [
6]. Therefore, a battery thermal management system is essential for EVs running on a uniform battery temperature under various conditions [
7], which aims to maintain an ideal average temperature between battery cells [
8].
In the battery thermal management system, the common ones are air-cooling heat dissipation [
9,
10], liquid cooling heat dissipation [
11,
12], phase change material heat dissipation [
13,
14,
15], and heat pipe heat dissipation [
16,
17,
18,
19]. However, air cooling is widely used in the Formula Electric Vehicle (FEV) with limited funds due to its simple structure and low cost. Air cooling relies on the continuous flow of cold air to pump the heat generated by the battery pack into the surrounding environment for better cooling performance [
20]. Mahamud et al. [
7] used a 2D CFD model to conduct numerical simulation analysis on the temperature influence of a cylindrical lithium ion battery under the action of reciprocating air flow. The research results showed that the reciprocating air flow could reduce the temperature of the battery system by 4 K in 72% of the batteries, and the temperature of the highest single battery could be reduced by 1.5 K compared with the one-way air flow. By comparing the hybrid passive thermal management system with the active thermal management system, Kermani et al. [
21] found that although the actively forced air convection reached a stable state below the safe temperature at 24 °C, the active and passive systems were ineffective at 40 °C.
In order to promote the development of battery-based new energy vehicles, Formula Student Electric China competition (FSEC) was jointly organized by the Chinese Society of Automotive Engineers in 2013. The competition items include endurance races and obstacle races. With this platform, more students dedicated to new energy research can take advantage of this opportunity to get more exposure to battery power technology. Due to the extremely fierce FSEC competitions, the internal temperature of the power battery of the electric racing car is also more severe than that of the ordinary passenger car. Therefore, the thermal analysis of the battery at the beginning of the design is particularly important. Since all the participants in the FSEC event are college students, it is necessary to deal with the thermal failure of the power battery and ensure that the manufactured cars comply with safety regulations.
This paper combines the simulations of the heat generation of cells and air-cooling heat dissipation of a battery pack with the discharge test of different power ratios in the race conditions, takes the heat management system of the FSEC battery as the research object, and selects the maximum temperature, the minimum temperature, and the maximum temperature difference as the optimization evaluation indexes to optimize and improve the structure of the air-cooling system.
Finally, the FSEC battery air-cooling system designed in this paper can effectively reduce the temperature accumulation of the battery under various working conditions, providing a certain technical reference for the further design of a pure electric racing car.
3. Design of Orthogonal Test Scheme for Heat Dissipation System
The thermal simulation results of the preliminary design of the air cooling heat dissipation system show that the maximum temperature difference of the system is still too large. Considering the heat dissipation defects of the preliminary design structure, it is necessary to seek the key factors and relevant levels that affect the heat dissipation effect of the FEV air cooling heat dissipation system and find the optimal and most reasonable design combination scheme.
In the orthogonal experimental scheme of the FEV air cooling and cooling system, 13 factors in
Table 2 are selected as considerations, the parameters of the selection factors in the preliminary design are comprehensively considered, and three levels are reasonably given. After consulting the orthogonal table specifications, an L27 (313) type orthonormal table was selected, and the related factors were numbered alphabetically, which are described in the following text. The maximum temperature, minimum temperature, and maximum temperature difference in the system were selected as the heat dissipation evaluation index.
In
Table 2, the single battery pack clearance parameter is given according to the sum of the thickness of the partition board and the clearance reserved in the actual design after simplifying the partition board. The specific horizontal parameter values of each factor are given according to the above table, and the specific design scheme of this FEV orthogonal experiment is given according to the L27 (313) orthogonal table selected. Detailed data are shown in
Table 3.