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The primary variable valve actuation strategies for diesel engines are variable late or early intake valve closing for control of effective compression ratio for Miller cycle and part-time HCCI, PCCI, or LTC; variable early exhaust valve opening for exhaust temperature control for after-treatment regeneration and improved engine transient response; on/off control of intake pre-bump and/or exhaust post-bump for IEGR and control of residual fraction; and on/off control of compression release and brake gas recirculation events for engine braking. Lost-motion hydraulic VVA is well suited to diesel engines due to the capability of on-off control of secondary events for IEGR and engine braking, high load capacity for early exhaust opening and engine braking, and inherent protection against valve-to-piston contact.

Internal exhaust gas recirculation (IEGR) with retarded injection timing can provide a 30% reduction in diesel nitrous oxide (NOx) emissions and is an attractive solution to meeting NOx emission levels in the range of 3.4-4.0 g/bkW-hr (2.5-3.0 g/bhp-hr) for heavy-duty diesel engines, especially for off-road and vocational applications. At lower NOx emissions levels, IEGR may be used to supplement cooled EGR or to control HCCI combustion. Alternative valve actuation strategies for IEGR are reviewed. A valve actuation system to provide on-off control of IEGR combined with compression-release braking is presented. System design and simulation results are reviewed. Engine performance predictions and initial test data are discussed, including turbocharger sizing and particulate emission considerations. System reliability is calculated using Weibull data from similar proven components.

Simulation tools are essential for the development of advanced engine braking and variable valve actuation systems. GT-Power with a valve lift user model, which includes effects such as valve-train compliance, is used to predict engine performance, valve lift, and cylinder pressure. MATLAB/Simulink with a hydraulic/valve-train dynamic library is used to evaluate factors relevant to system design such as hydraulic circuit pressures, cam follow, valve-seating velocity, and parasitic loss. CFD is used in hydraulic component design and to provide flow resistance data for the system simulation. FEA is used together with the system simulation to evaluate the design durability, including prediction of impact loads. These tools have been applied to the development of a wide range of compression-release braking and variable valve actuation systems, including recent lost-motion and common-rail designs.