# Equivalent Simulation Study of Delta-Rotor Engine
## 1 Introduction  
Since the birth of the delta-rotor engine in the last century, its advantages such as high-power density, a simple structure, a small size, and a light weight have attracted the attention of countries worldwide (Kong and [PERSON], 2021) [1]. In the 21 st century, with the increasing demand for various types of miniaturised, intelligent, and unmanned vehicles, rotary engines have become the best choice for various unmanned aerial vehicles (UAVs) and cruise missiles ([PERSON], 2021; [PERSON], 2022; [PERSON] and [PERSON], 2023) [2; 3; 4]. However, owing to market demand, the most commonly used commercial software (2022.1) such as AVL's FIRE, Ricardo's WAVE, and GTI's GT-SUITE do not have direct modelling and simulation capabilities for triangular rotor engines. This is because the mechanical structure, movement mode, intake and exhaust structure, and combustion process of the triangular rotor engine are different from those of conventional engines; therefore, it cannot be directly modelled, and other simulation software attempts for triangular rotor engines cannot meet current research and development needs, owing to their early development time ([PERSON] and [PERSON], 2023) [5]. Currently, two main methods are used to simulate the performance of the delta-rotor engine in the development stage: using special software for modelling a simulation, or treating the delta-rotor engine as equivalent to a conventional engine and modelling a simulation using commercial software. The former usually requires a large amount of experimental data as support for modelling analysis, which leads to poor versatility among different models. Moreover, newly developed software requires large investments, leading to an excessively long development phase ([PERSON], 1974; [PERSON], 1976; [PERSON], 2006) [6; 7; 8]. The latter has been proven to be able to achieve the purpose of modelling triangular rotorengines through some equivalent substitutions ([PERSON] and [PERSON], 1995; [PERSON], 2015; [PERSON], 2017; [PERSON] et al., 2012; [PERSON], 2016) [9; 10; 11; 12; 13]. [PERSON] first simulated a rotary engine using non-commercial software ([PERSON], 1983) [14]. [PERSON] et al. used GT-SUITE to establish a simulation model of a triangular rotor engine and studied its intake and exhaust processes ([PERSON] et al., 2012) [15]. [PERSON] et al. used equivalent methods to study the impact of multiple fuel gas mixtures on the combustion process of a rotary engine ([PERSON] et al., 2020) [16]. [PERSON] et al. used AVL BOOST's module designed for the triangular rotor engine to establish a one-dimensional simulation model and comprehensively studied the impact of injection pressure and injector position on engine performance at different speeds ([PERSON] et al., 2018) [17]. [PERSON] et al. used AVL BOOST to establish a one-dimensional simulation model and compared the fuel consumption and emission results of the simulation model and test at different speeds ([PERSON] et al., 2018) [18]. However, the aforementioned studies have shortcomings and do not comprehensively consider the unique movement mode, intake and exhaust structure, and combustion process of rotary engines. The established equivalent models were not compared or calibrated, and key indicators such as the cylinder temperature, cylinder pressure, and in-cylinder mass were not compared to verify the correctness and accuracy of the models. This brings difficulties to the establishment of the equivalent model of the triangular rotor engine, making it difficult to conduct structural evaluation and performance prediction of the engine during the development stage ([PERSON], 2005; [PERSON] et al., 1978) [19; 20]. To solve these problems, this study comprehensively considers the movement mode, intake and exhaust structures, and combustion process of a triangular rotor engine.