## 1 Introduction
About 19-25% reduction in NOx emission was obtained for a 6-cylinder 7.3 L turbocharged diesel engine without aftertreatment under CDA operation [32]. This is attributed to the fact that the decreased boost pressure in the compressor, caused by the increased backpressure before the turbo inlet under CDA operation, results in a reduction in the amount of fresh air charged and accordingly less oxygen in the active cylinder. Moreover, the increased emissions can be compensated by EGR and aftertreatment [23; 34]. CDA improves the performance of the aftertreatment system by increasing the exhaust gas temperature [35; 36; 37; 31]. In order to ensure the efficient operation of the aftertreatment system, its temperature must reach approximately 250 \({}^{\circ}\)C [23]. The increment of exhaust gas temperature under CDA operation ranges from 62 to 150 \({}^{\circ}\)C [24]. A transient test of a 6-cylinder Cummins diesel engine with CDA, implemented through a camless variable valve actuation system, has shown that during extended idle operation with CDA, the emissions of soot and NOx were reduced by 72% and 52%, respectively, associated with fuel savings up to 40% [38]. From the above literature analysis, it can be concluded that the effect of CDA introduction to a large extent depends on engine configurations, operation points, and CDA strategies, and most of the performed research relates to SI engines and high-speed CI engines for vehicles and road transport. However, there is insufficient data about investigating and applying CDA in medium-speed high-power CI engines until now. The medium-speed CI engines will maintain their important role in a long term in maritime business and railway transports [39; 40; 41]. It is also highly meaningful to improve the performance of the existing engines. Medium-speed high-power diesel engines of rail traction locomotives with series 8, 12, 16 cylinders have a wide output power range, whose rated power might exceed 2000 kW. According to locomotive operation characteristics, traction locomotives may run at multi-start/stop status or stay idle for a long time and only in a limited percentage of the time (about 10%) at full power mode [41], which leads to fuel energy losses. In addition, idle and start/stop processes are characterized by low engine efficiency, high specific fuel consumption, and exhaust emissions deterioration [42]. In such cases, CDA can be of great practical value. The objective of the study is to evaluate the effectiveness of introducing CDA to medium-speed high-power CI engines by BSFC and emission level analysis. A thermodynamic engine model coupled with a dynamic mechanical system based on a turbocharged 16-cylinder diesel engine D-49 with CDA operations has been developed to investigate the effect of CDA on engine performance (including the indicated efficiency and mechanical losses in the active and deactivated cylinders). Although the technology of Rolling CDA or Dynamic Skip Fire could bring more fuel saving benefits and improve NVH characteristics under CDA operation [9], the fixed CDA is a more appropriate method for the large-scale diesel engine D-49, because most electric-hydraulic valve systems have a slow response, but the high-response electromagnetic valve system is impossible to be used for large inertia systems [9; 43]. From this point of view, in the present study, fixed CDA is applied to the investigated diesel engine. Two CDA modes were considered here: only cutting off the fuel supply; cutting off the fuel supply and disabling valves in deactivated cylinders. In order to achieve an accurate assessment of the impact of CDA on engine emission characteristics, a 3D CFD combustion model has been created and used.