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Gasoline Full Hybrid Electric Vehicles (FHEVs) are considered among good candidates as cost-effective solution to comply with upcoming emissions legislation. However, several studies have highlighted that frequent start-and-stops worsen the hydrocarbon tailpipe emissions, especially when the light-off temperature of the three-way catalyst (TWC) has not been reached. In fact, strategies only addressing the minimization of fuel consumption tend to delay engine activation and hence TWC warming, especially during urban driving. Goal of the present research is therefore to develop an on-line powertrain management strategy accounting also for TWC temperature, in order to reduce the time needed to reach TWC light-off temperature. A catalyst model is incorporate into the model of the powertrain where torque-split is performed by an adaptive equivalent consumption minimization strategy (a-ECMS). The developed a-ECMS operates on a domain of power-split combinations between electric machine and internal combustion engine, which, aside from satisfying the torque demand, also ensure a controlled ICE torque derivative as well as a controlled ICE start-and-stop frequency. Hence, the algorithm, which is extended for TWC thermal management, incorporates a penalty on the deviation of the TWC temperature from its optimal temperature range. The strategy has been tested on a gasoline P2 FHEV platform whose components (internal combustion engine, electric machine, battery and three-way catalyst) have been experimentally characterized. In particular, the battery current limitations have been modelled as a function of energy transfer. The effects deriving from the strategy, in terms of fuel consumption and catalyst efficiency, have been analyzed on the WLTC (Worldwide harmonized Light vehicles Test Cycles), the new homologation cycle enforced by European legislation. The control algorithm enhances a sufficient catalyst heating within a timespan comparable to the one of a conventional ICE case. The control strategy that integrates TWC thermal anagement causes an increase of about 2% in fuel consumption, compared to an only fuel economy-oriented a-ECMS strategy.

Emission control efficiency and limited fuel consumption penalty and are the main design factors driving the development of engine-after-treatment exhaust systems according to both ACEA/DOE targets and continental regulations. The particulate-filter is certainly a critical technology to this aim as usually presents very high pm reduction efficiencies (even more than 90% on a mass basis depending on soot loading) leading however to a back pressure increase and eventually to an appreciable fuel consumption penalty. Nevertheless, it is in general discussion that health hazard related to particulate depends primarily on total number of emitted particles rather than on mass. The partial-flow-filter has been recently developed presenting lower reduction efficiencies on a mass basis but also a reduced penalty on fuel consumption. As a selective capability of this filter in capturing the smaller particles has also been experimentally observed, technological and scientific interest in the development of design and analysis tools dedicated to this technology has developed. However, traditional 1D and 2D models cannot be directly applied to study this technology, as the coupling between fluid-dynamics and filtration must be properly taken into account by exactly modeling single channel geometry as it is. Thus, in order to represent filtration effects by varying diameter class in partial-flow-filters, a 3D model has been coupled to a phenomenological filtration submodel taking into account Brownian diffusion and interception phenomena within an Eulerian transport framework for different particle classes depending on diameter. Results have been compared to experimental data and state that the model is able to represent the main occurring fluid-dynamic and filtration phenomena by varying mass flow rate and particle diameter.

The design of compact and efficient Diesel Oxidation Catalysts (DOC) is primarily important to comply with emission regulations not increasing engine fuel consumption at the same time. To design DOCs, Sherwood number correlations are typically used to calculate mass transfer by varying operating conditions in terms of catalyst volume, active area and mass flow rate. To that aim, Sherwood number trend over channel length has been extensively studied during last decades. However, Sherwood number correlations are highly dependent on channel geometry, and on the possible presence of special structures (such as blades, fins or bumps). These modifications, which characterize the latest developments in substrate technology, allow to improve mass transfer performance and require a special characterization. In this paper, a joint experimental/3D-numerical approach is used to study the role of special structures, and namely of LS (Longitudinal Structure) blades, on mass transfer mechanism inside a DOC. It is proved that the generation of unsteady/turbulent flow structures due to the inclusion of blades is essential in LS substrate, and leads already at Re in the order of 700 to an under-estimation of the performance by using a steady state laminar 3D model. Re dependent Sherwood correlations are then proposed for standard and LS substrates, to calculate mass transfer between the bulk and the wall of a given channel by varying operating conditions (channel length, channel density, mass flow rate) taking also into account unsteady/turbulent effects.

The use of hydrogen (H2) as a fuel for urban private and public transport may represent a major solution to reduce pollutant emissions and CO2 production in urban areas. Looking for short-term solutions, the introduction of moderate quantities of H2 (up to 30%)into Natural Gas (NG) SI engines may be a feasible solution to get a faster combustion process, and therefore less HC and CO2 emissions, and a slight NOx increase which may be potentially limited by the adoption of lean-burn engine control strategies. However, concurrent effects of volumetric efficiency reduction and maximum temperature in the combustion chamber require a careful optimization of operating conditions to fully exploit the H2 potential and to determine the most convenient H2/NG mixture ratio. In that context, 3D numerical tools may be useful to analyze the effect of H2 introduction on engine performance. Combustion modelling should be handled with care, since performance variation mainly depends on fuel properties (heating value, laminar flame speed) and on the effect of turbulent transport on the global turbulent flame speed. In this paper, results concerning a project (BONGHY) to introduce H2/NG fuel mixtures into a public transport fleet are reported. Project BONGHY activities have been carried out in conjunction with ENEA, ASM and Universities of Roma La Sapienza and Cattolica di Brescia, to analyze the H2/NG mixture potential as a fuel for garbage trucks in urban areas. Results here reported particularly concern numerical activities to predict the effect of H2 introduction on final engine performance. To that aim, KIVA-3V code has been utilized as the basic thermal-fluid-dynamic platform where an advanced combustion model (CFM) based on the flamelet assumption and suitably modified to support H2/NG mixture combustion has been implemented.

The correct simulation of combustion process allows to better face several SI engines design problems, not only for innovative mixture formation concepts (stratified or ultra-lean charge), but for traditional homogeneous mixture as well. Even though many commercial codes are able to describe the complex 3-D non reacting fluid dynamics in ICE, the simulation of high turbulent flame propagation does not seem to be a completely solved problem yet. In this work a comparison between two different turbulent combustion models (a characteristic time based one by Abraham and Reitz [2, 15, 16] and a flamelet based one by Cant and AbuOrf [4, 20]) has been performed using KIVA-3V code to assess simulation reliability. Models predictive capabilities have been tested with reference to specific data acquired at the engine test bench of Tor Vergata Mechanical Engineering Department on a Fiat Punto 1242 cc 8 valves SI engine over a wide range of operating conditions.