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The low-NOx standard for heavy-duty trucks proposed by the California Air Resources Board will require rapid warm-up of the aftertreatment system. Several different engine technologies are being considered to meet this need. In this study, a 1-D engine model was first used to evaluate several individual control strategies capable of increasing the exhaust enthalpy and decreasing the engine-out NOX over the initial portion of the cold start FTP cycle. The additional fuel consumption resulting from these strategies was also quantified with the model. Next, several of those strategies were combined to create a hypothetical aftertreatment warm-up mode for the engine. The model was then used to evaluate potential benefits of an air gap manifold (AGM) and two different turbine by-pass architectures. The detailed geometry of the AGM model was taken into account, having been constructed from a real prototype design.

Diesel particulate filters with a quantity of ash corresponding to the service interval (4500 hours) are needed to verify that soot loading model predictions remain accurate as ash accumulates in the DPF. Initially, long-term engine tests carried out for the purpose of assessing engine and aftertreatment system durability provided ash-loaded DPFs for model verification. However, these DPFs were found to contain less ash than expected based on lube oil consumption, and the ash was distributed uniformly along the length of the inlet channels, as opposed to being in the form of a plug at the outlet end of those channels. Thus, a means of producing DPFs with higher quantities of ash, distributed primarily as plugs, was required. An engine test protocol was developed for this purpose; it included the following: 1) controlled dosing of lube oil into the fuel feeding the engine, 2) formation of a soot cake within the DPF, and 3) periodic active regenerations to eliminate the soot cake.

The accumulation of ash in a Diesel Particulate Filter (DPF) eventually results in an increase in the pressure drop across the exhaust system component. This situation translates into a reduced capacity for soot, and requires an increased frequency of active regenerations to eliminate this soot. For heavy duty diesel applications, the lifetime of the DPF is long enough to expect that cleaning of the ash from the DPF will be required. The physico-chemical characteristics of the ash as a function of temperature and time will have an impact on the effectiveness of this cleaning. To develop a deeper understanding of this subject, four different samples of ash were characterized in this study that were collected under active or passive regeneration from exhaust systems of engines running on different fuels: ultra low sulfur diesel (ULSD), and biodiesel fuels B20 and B100. The lubricant, an API CJ-4 oil, was used for each engine test.