Development and Testing of a Concentric Tube Camshaft for Continuous Adjustment of Intake Valve Duration and Timing in Otto and Miller Cycle Operations

The development of technologies capable of expanding the operational flexibility of internal combustion engines—particularly through advanced valve actuation strategies—has become essential for improving energy efficiency and reducing exhaust emissions. This work presents the design, manufacturing, and experimental evaluation of a novel, mechanically simple, and low-cost valve control system intended for spark-ignition engines originally designed to operate under the Otto cycle. The proposed innovation, designated VVT-D (Variable Valve Timing—Duration), introduces continuous and independent control of intake valve opening duration using a concentric tube camshaft architecture. Unlike conventional variable valve timing systems limited to phase control, the VVT-D concept enables continuous transition between Otto- and Miller-equivalent operating conditions by modulating intake valve duration as a function of engine load. This approach allows engine load control via Late Intake Valve Closing (LIVC), partially or fully eliminating intake throttling (dethrottling) and thereby reducing pumping losses, particularly under low- and medium-load conditions. The system was implemented in a Volkswagen EA211 1.0 TSI engine and evaluated on an engine dynamometer under torque-matched operating conditions. Experimental results demonstrated proper system functionality, mechanical robustness, and effective load modulation capability through intake valve duration variation. Under Miller-equivalent operation, a reduction of approximately 15.6% in brake-specific fuel consumption (BSFC) was observed relative to conventional throttled Otto cycle operation at partial load. These results indicate that the proposed VVT-D system provides meaningful improvements in overall engine efficiency while preserving the original engine architecture and offering a cost-effective alternative to fully variable or purely hydraulic valve actuation systems.