Thermal inhomogeneity and physical processes like fluid dynamics reduce the utility of rapid compression machine (RCM) facilities to accurately study fuel combustion phenomenon relevant to internal combustion engines. Most current RCMs incorporate a large crevice volume in the piston to capture roll-up vortices that encroach into the combustion zone during compression. In this work, a bowl piston design similar to those used in diesel engines is proposed as an alternative to enlarged creviced pistons for creating a sufficiently thermally homogenous gas mixture prior to ignition without undesirable fluid motion found in flat piston configurations. The bowl piston also eliminates the possibility of cold unreacted gases entering the combustion chamber when the piston is retracted in rapid compression and expansion machines (RCEMs) like in creviced piston designs. In the work, a bowl piston was compared to creviced piston and flat piston configurations numerically and experimentally. Through non-reacting computational fluid dynamics simulations, the bowl piston reduced the roll-up vortex found for the flat piston and led to a higher temperature and more thermally uniform core of gas at peak compression compared to the enlarged crevice piston. Experimentally, three pistons were studied in a RCM facility with ethanol and n-butane as fuels. Results showed that the bowl piston yielded benefits over conventional piston geometries including: reduced heat loss due to lower surface area, higher turbulent Reynolds Number, stronger ignition, and higher heat release rate and combustion efficiency as estimated using heat release analysis. Based on the findings presented here, we conclude that bowl piston geometries are a promising alternative to creviced pistons for conducting fuel ignition studies in RCM and RCEM facilities.

热不均匀性和物理过程（例如流体动力学）降低了快速压缩机（RCM）设施精确地研究与内燃机相关的燃料燃烧现象的效用。当前大多数RCM在活塞中都包含较大的缝隙，以捕获在压缩过程中侵入燃烧区的卷起涡流。在这项工作中，提出了一种碗形活塞设计，该碗形活塞设计类似于柴油发动机中使用的碗形活塞，以替代扩大的活塞，以在点火之前产生足够热均匀的气体混合物，而在扁平活塞配置中不会出现不希望的流体运动。碗形活塞还消除了当活塞在快速压缩和膨胀机（RCEM）中缩回时（如在弯曲活塞设计中一样）时，未反应的冷气体进入燃烧室的可能性。在工作中，在数值上和实验上将碗形活塞与弯曲活塞和扁平活塞配置进行了比较。通过无反应的计算流体动力学模拟，与扩大的缝隙活塞相比，碗形活塞减少了扁平活塞发现的上旋涡流，并在峰值压缩时导致更高的温度和更均匀的气体核心。通过实验，在RCM设施中使用乙醇和乙醇对三个活塞进行了研究。通过无反应的计算流体动力学模拟，与扩大的缝隙活塞相比，碗形活塞减少了扁平活塞发现的上旋涡流，并在峰值压缩时导致更高的温度和更均匀的气体核心。通过实验，在RCM设施中使用乙醇和乙醇对三个活塞进行了研究。通过无反应的计算流体动力学模拟，与扩大的缝隙活塞相比，碗形活塞减少了扁平活塞发现的上旋涡流，并在峰值压缩时导致更高的温度和更均匀的气体核心。通过实验，在RCM设施中使用乙醇和乙醇对三个活塞进行了研究。正丁烷为燃料。结果表明，碗形活塞比传统的活塞几何形状更具优势，包括：由于表面积减小而减少的热损失，更高的湍流雷诺数，更强的点火力以及通过放热分析估算出的更高的放热率和燃烧效率。根据此处提出的发现，我们得出结论，对于在RCM和RCEM设施中进行燃料点火研究，碗形活塞的几何形状是有前途的活塞的有前途的替代方案。