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One way to achieve low temperature regeneration on diesel particulate traps is to employ NO2 as the oxidant. However, the engine may not produce sufficient NOx to achieve the required particulate regeneration. An RRT (rolling regeneration trap) was proposed as a way to enhance the effective concentration in diesel engine exhaust. The RRT uses catalyzed ceramic foam, which allows repeated use of existing NOx in the exhaust stream. The ceramic foam is a filter itself: thus, it can reduce the particulate loading on the wall-flow filter, which is more prone to plugging by the particulate deposits. Furthermore, the presence of particulate matter in the catalyzed section circumvents the high temperature limit imposed by thermodynamic equilibrium of a simple NO+NO2 +O2 system. However, experimental results revealed that the regeneration efficiency on the wall-flow section was very low and NO2 slip is an issue.

This study is a continuing effort toward the goal of understanding deposit formation process in a combustion chamber by probing the impacts of engine operating conditions and fuel compositions on the formation of combustion chamber deposits. To facilitate the study, four retrievable deposit sampling probes were used. The engine operating parameters investigated include coolant temperature, spark advance, manifold air pressure (engine load), and fuel-air ratio. As a continuum of previous studies, toluene was used as the base fuel. In addition, CCD-forming tendencies of isooctane and other aromatics with higher boiling points were investigated. Coolant temperature, fuel-air ratio, and boiling point of the fuel have significant impacts on both the amount and the morphology of deposits formed in a combustion chamber. In contrast, spark advance has little impact on either deposit weight or deposit morphology. Manifold pressure has an intermediate impact on CCD.

Growing concern about the impact of combustion chamber deposits (CCD) on engine performance and exhaust emissions has renewed interest in understanding the deposit formation process in a combustion chamber. To provide a true picture of the deposit formation process, an extensive micrographic study of the deposits in a single cylinder engine has been conducted. Four retrievable deposit sampling probes were used. The sampling period for the deposits varied from 15 minutes to 20 hours to show how the deposits evolved with time. The coolant temperature was changed from 50°C to 95°C to observe the effect of surface temperature on deposit morphology. Impacts of deposit control additives on the deposit distribution and deposit morphology were also investigated. Deposits formed in different parts of the combustion chamber differed significantly in their morphology. The differences occur mainly because of variations in surface temperature.

Combustion chamber deposits in an internal combustion engine are known to impair engine performance. Using a variable temperature probe and retrievable sampling coupons, this study shows that the deposit-forming rate is inversely related to surface temperature, and directly related to the stabilized deposit weight. Together with the well-recognized fact that deposits are good thermal insulators, a deposit-forming mechanism is proposed. As combustion chamber deposits form, in essence the chamber surface is coated with thermal insulators, layer after layer. Consequently, the surface temperature will rise as the deposit grows. The previously derived critical surface temperature of 310°C is found to be valid in this study for fuel-derived deposits. Furthermore, a critical surface temperature also exists for oil-derived deposits, except that the critical surface temperature is about 60°C higher than that for fuel-derived deposits.

Short deposit sampling procedures were employed in a single-cylinder CFR engine to investigate the potential which an engine oil or an oil component has for forming deposits. Both valve temperature and oil flowrate on a valve have significant effects on an oil's deposit forming tendency. However, the formulation of the oil is the dominating factor that determines whether an oil will keep a valve clean or form heavy deposits. Among the oil components, oil detergents, dispersants, and VI improvers are major contributors to intake valve deposits, while high-boiling base oil can keep a valve clean. The deposit forming tendency of an oil in a combustion chamber is very different from its tendency to form deposits on an intake valve. Higher oil consumption rates and higher base oil boiling ranges tend to increase the deposit level in a combustion chamber.