The lowered combustion temperature in diesel engines is capable of reducing nitrogen oxides and Soot Simultaneously, which call be implemented by the heavy use of exhaust gas recirculation (EGR) or the homogeneous charge compression ignition (HCCI) type of combustion. However, the fuel efficiency of the low-temperature combustion (LTC) cycles is commonly compromised by the high levels of hydrocarbon and carbon monoxide emissions. More seriously, the scheduling of fuel delivery in HCCI engines has lesser leverage on the exact timing of auto-ignition that may even occur before the compression stroke is completed, which may cause excessive efficiency reduction and combustion roughness. New LTC control strategies have been explored experimentally to achieve ultralow emissions under independently controlled EGR, intake boost, exhaust backpressure, and multi-event fuel-injection events. Empirical comparisons have been made between the fuel efficiencies of LTC and conventional diesel cycles. Preliminary adaptive control strategies based on cylinder pressure characteristics have been implemented to enable and stabilize the LTC when heavy EGR is applied. The impact of heat-release phasing, duration, shaping, and splitting on the thermal efficiency has also been analyzed with engine cycle simulations. This research intends to identify the major parameters that affect diesel LTC engine thermal efficiency. Copyright (C) 2008 John Wiley & Soils. Ltd.