Experimental analysis on the operation process of opposed-piston free piston engine generator

As a novel energy conversion device, opposed-piston free piston engine generator (FPEG) has high energy conversion efficiency, high power density, low heat transfer loss and excellent NVH performance. The opposed-piston FPEG test platform is built, and the continuous and stable operation of the prototype is realized. The influence laws of key parameters such as fuel injection timing, ignition timing, fuel injection quantity, scavenging pressure and rebound cylinder initial pressure on the performance of the system are systematically analyzed, the suitable value for the opposed-piston FPEG is determined, and the stable operation mechanism and synchronization error of the system are analyzed. It is found that there is a matching relationship between injection timing and ignition timing. The injection position should be set at 37 mm-39 mm, the ignition position should be 25–27 mm, and the injection and ignition interval should be controlled at about 12 mm. The peak in-cylinder pressure increases with the increase of fuel injection quantity, and the fuller the P-V diagram is. When the scavenging pressure is 1.5 bar and the ignition position is 25 mm-27 mm, the basic indexes have extreme points. When the ignition position is 27 mm, the peak in-cylinder pressure is the largest and the engine indicated thermal efficiency is the highest. When the initial pressure of rebound cylinder is 1.7 bar, the indicated thermal efficiency is the highest. Under the trajectory tracking control strategy, the system realizes continuous and stable operation and can deal with large cylinder pressure fluctuation. The synchronization error changes periodically and is relatively large in the middle of the expansion stroke and near the outer dead center.