Vittorio Rocco

1D-3D Analysis of the Scavenging and Combustion Process in a Gasoline and Natural-Gas Fuelled Two-Stroke Engine

The paper presents a 1D-3D numerical model to simulate the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. The engine is crankcase scavenged and can be operated with both gasoline and Natural Gas (NG). The analysis is performed with a modified version of the KIVA3V code, coupled to an in-house developed 1D model. A time-step based, two-way coupled procedure is fully described and validated against a reference test. Then, a 1D-3D simulation of the whole two-stroke engine is carried out in different operating conditions, for both gasoline and NG fuelling. Results are compared with experimental data including instantaneous pressure signals in the crankcase, in the cylinder and in the exhaust pipe. The procedure allows to characterize the scavenging process and quantify the fresh mixture short-circuiting, as well as to analyze the development of the NG combustion process for a diluted mixture, typically occurring in a two-stroke engine. Results in terms of performance and emission characteristics of this engine are presented and discussed.

Spent coffee enhanced biomethane potential via an integrated hydrothermal carbonization-anaerobic digestion process

This study reports the implications of using spent coffee hydrochar as substrate for anaerobic digestion (AD) processes. Three different spent coffee hydrochars produced at 180, 220 and 250 °C, 1 h residence time, were investigated for their biomethane potential in AD process inoculated with cow manure. Spent coffee hydrochars were characterized in terms of ultimate, proximate and higher heating value (HHV), and their theoretical bio-methane yield evaluated using Boyle-Buswell equation and compared to the experimental values. The results were then analyzed using the modified Gompertz equation to determine the main AD evolution parameters. Different hydrochar properties were related to AD process performances. AD of spent coffee hydrochars produced at 180 °C showed the highest biomethane production rate (46 mL CH4/gVS.d), a biomethane potential of 491 mL/gVS (AD lasting 25 days), and a biomethane gas daily composition of about 70%.

Biomass furnace study via 3D numerical modeling

Purpose – In the recent years the interest toward the use of biomass as a fuel for energy conversion, along with the continuous tightening of regulations, has driven the improvement of accurate design techniques which are required to optimize the combustion process and simultaneously control pollutant emissions. In this paper the use of a 3D Computational Fluid Dynamics approach is analyzed to that aim by means of an application to an existing 50 MW biomass fixed-bed combustion furnace fueled by grape marc. The paper aims to discuss these issues. Design/methodology/approach – The studied furnace is an interesting example of biomass utilization as it may integrate biomass with organic residual by an industrial process. The numerical model has been implemented into an OpenFOAM solver, with an Eulerian-Lagrangian approach. In particular, the fully 3D approach here presented, directly solves for the gas and solid evolution in both the combustion bed and the freeboard. Special care has also been devoted to the...

Particle Number Emissions: An Analysis by Varying Engine/Exhaust-System Design and Operating Parameters

An increasing concern has been growing in the last years toward health effects due to Particulate Matter (PM) emissions. This triggered the widespread diffusion of Diesel Particulate Filters (DPFs), which equip almost every Diesel car and truck on the market, allowing to get large reduction (in the order of 95% and more) in terms of PM mass. However, PM health effects are believed to be more related to particle number rather than to particle mass. This gave rise in Europe to new regulations for passenger cars on total particle number, that will be introduced from EURO6 on. Engine/Exhaust-System assembly is therefore under investigation, to better understand the effectiveness of aftertreatment components toward particle number reduction, especially by varying engine and exhaust-system design/ operating conditions, and to compare particle number emissions to particle mass emissions. Given the background, an experimental study on particle emissions of a FIAT 2.01 EURO5 passenger car Diesel engine coupled to a DOC-DPF system is proposed in this paper. Experimental data have been gathered at the engine test bench of the University of Rome Tor Vergata. Data have been acquired with regard to ECE-EUDC representative steady state engine operating points, to highlight correlations among specific engine operating conditions and upstream/ downstream DPF particle number distribution and mass. Special attention has been devoted to the analysis of three different DPF materials and specifications toward particle emissions, both in terms of mass and number, during the transient loading and regeneration processes, as well as during steady state operating conditions after DPF preconditioning. Moreover, effects related to the variation of key engine operating parameters, such as EGR and pressure injection, have been analyzed.

Biomass pyrolysis modeling of systems at laboratory scale with experimental validation

Purpose Thermochemical conversion processes are one of the possible solutions for the flexible production of electric and thermal power from biomass. The pyrolysis degradation process presents, among the others, the interesting features of biofuels and high energy density bio-oil production potential high conversion rate. In this paper, numerical results of a slow batch and continuous fast pyrolyzers, are presented, aiming at validating both a tridimensional computational fluid dynamics-discrete element method (CFD–DEM) and a monodimensional distributed activation energy model (DAEM) represents with data collected in dedicated experiments. The purpose of this paper is then to provide reliable models for industrial scale-up and direct design purposes. Design/methodology/approach The slow pyrolysis experimental system, a batch of small-scale constant-pressure bomb for allothermic conversion processes, is presented. A DEM numerical model has been implemented by means of a modified OpenFOAM solver. The fast pyrolysis experimental system and a lab scale screw reactor designed for biomass fast pyrolysis conversion are also presented along with a 1D numerical model to represent its operation. The model which is developed for continuous stationary feeding conditions and based on a four-parallel reaction chemical framework is presented in detail. Findings The slow pyrolysis numerical results are compared with experimental data in terms of both gaseous species production and reduction of the bed height showing good predictive capabilities. Fast pyrolysis numerical results have been compared to the experimental data obtained from the fast pyrolysis process of spruce wood pellet. The comparison shows that the chemical reaction modeling based on a Gaussian DAEM is capable of giving results in very good agreement with the bio-oil yield evaluated experimentally. Originality/value As general results of the proposed activities, a mixed experimental and numerical approach has demonstrated a very good potential in developing design tools for pyrolysis development.

Particle Number and Mass Collection Efficiencies in a Close-Coupled DOC-DPF System: Experimental Analysis Supported by Soot Load Modeling

PM effects on health are believed to be more related to particle total number rather than to particle total mass. This gave rise in Europe to the forthcoming introduction of an emission standard on total particle number, that will take place for passenger cars from EURO5 (stage b) on. The behavior of the DPF is therefore under investigation, to better understand its effectiveness toward particle number reduction. Moving from that background, a study on the effect of a close coupled DOC-CDPF (Diesel Oxidation Catalyst + Catalyzed Diesel Particulate Filter) on PM emissions is proposed in this paper, with special focus on the comparison between mass and number collection efficiency. Experimental data have been gathered at the engine laboratory of the University of Rome Tor Vergata, equipped with a FIAT 2.0l EURO 5 passenger car engine. Data have been acquired with a TSI 3090 EEPS to measure particle distribution and total number, and an AVL-415 S to measure PM mass emissions. A numerical code has been also developed to represent the DPF behavior, in terms of soot load (g/l) trend, under forced regenerating operating conditions and better understand regeneration potential as a function of time. Results, acquired for three non regenerating and one forced regenerating modes, prove that mass and number efficiencies are close to 100%, with a slight decrease during the forced regeneration mode.Copyright

An Analysis of 3D Simulation of SI Combustion with an Improved Version of the Kiva 3V Code: Numerical Formulation and Experimental Validation

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.

Trip-based control strategy for simple and efficient use of plugin hybrid electric vehicles

The optimal management of plugin hybrid electric vehicles (PHEVs) energy efficiency and range autonomy is strictly dependent on the battery discharge rate which may be expressed by its state of charge (SOC) time variation. In fact, vehicle efficiency is strongly influenced by the possibility of controlling the SOC discharge rate as well as of the trip distance and the availability of recharging facilities along the itinerary. In the given scenario, the accurate control of SOC discharge rate to complying with trip-based target values of the SOC (which allow for taking into account the availability of external recharge station opportunities) appears as a key aspect to be investigated. In this paper, we propose a robust and efficient optimised control strategy, implementable in a state of the art ECU. The power-split strategy may be defined for any given trip also taking into proper account the vehicle speed over the route. The main target demonstrated in this paper is the request of reaching a target SOC (SOCL) at the end of the trip although the application to other objectives (e.g., minimisation of emissions) is also theoretically feasible. The proposed strategy is implemented and tested in a PHEV vehicle model designed and realised at the University of Rome Tor Vergata, and validated by using experimental data directly acquired over several standard cycles and real-world routes.

Effects of Biodiesel Distillation Process of Waste Cooking Oil Blends on Particle Number and Mass Emissions

The use of biodiesel has been widely accepted as an effective solution to reduce greenhouse emissions. The high potential of biodiesel in terms of PM emission reduction may represent an additional motivation for its wide diffusion. This potential is related to the oxygenated nature of biodiesel, leading to a different PM-NOx trade-off. Wide diffusion is also under debate as it may represent a solution to the highly disputed issue of the development of alternative biofuels sources not competing with the food chain. In fact, besides second generation biofuels (e.g. from algae), the transesterification of Waste Cooking Oil (WCO) is another option, that however needs additional insight. In fact, in this case, the effects on particle emissions are still not well assessed, as well as the impact of fuel distillation on engine performance and emissions.In this paper an experimental study on particle emissions of a DEUTZ 4L off-road Diesel engine coupled to a DOC-DPF system is proposed. Experimental data have been gathered at the engine test bench of the University of Rome Tor Vergata, by using baseline fossil fuel (B06) and blends (30% vol) with both distilled and non distilled WCO biodiesel. Data have been acquired with respect to the three most probable engine points referring to the NRTC (Non-Road-Transient-Cycle), upstream and downstream of the AfterTreatment System.Results show that B30 fuels have always lower emission on a mass and number basis, and that distillation process may have an impact especially at high power and torque operation. A slightly better behavior in terms of mass emissions has been observed for the blend with distilled fuel, while a slightly better behavior in terms of particle number has been observed for the blend with non-distilled fuel.Copyright

Image Processing for Early Flame Characterization and Initialization of Flamelet Models of Combustion in a GDI Engine

Ignition and flame inception are well recognised as affecting performance and stable operation of spark ignition engines. The very early stage of combustion is indeed the main source of cycle-to-cycle variability, in particular in gasoline direct injection (GDI) engines, where mixture formation may lead to non-homogenous air-to-fuel distributions, especially under some speed and load conditions. From a numerical perspective, 3D modelling of combustion within Reynolds Averaged Navier Stokes (RANS) approaches is not sufficient to provide reliable information about cyclic variability, unless proper changes in the initial conditions of the flow transport equations are considered. Combustion models based on the flamelet concept prove being particularly suitable for the simulation of the energy conversion process in internal combustion engines, due to their low computational cost. These models include a transport equation for the flame surface density, which needs proper initialization. A flame collocation is indeed to be properly made when starting the calculations, often just based on the users skill and without resorting to any quantitative data derived from experiments. However, the way to define initial conditions for cyclic variability prediction is often based on just statistical considerations. This work aims at exploiting information derived from images collected in a single cylinder 4-stroke GDI engine to properly collocate the flame at the start of the combustion calculation. The considered engine is optically accessible through a wide fused-silica window fixed on the piston crown having a Bowditch design. Image processing methodologies are applied to evaluate local and integral luminous intensity, and flame morphology parameters. The collected data allows improving the numerical simulation and gaining hints about the main parameters defining the engine cyclic variability.