Search Results

The dynamic effects of a coolant flow rate variation on knock tendency are experimentally investigated on a small S.I. engine. The analysis concerns the transient response of the unburned gas temperature and the knock onset to a step variation in load and coolant flow rate. This phenomenological investigation aims at preventing knock through a proper thermal management as an efficient alternative to the currently adopted strategies. Moreover, the proposed approach may result particularly useful for hybrid-electric powertrain, where the engine is expected to operate in the highest efficiency region by adopting high compression ratios and full stoichiometric map. The analysis is carried out through an experimental campaign, where the control of cylinder wall temperature is achieved by means of an electrically driven water pump. The spark advance and the air/fuel ratio have been properly varied in order to operate with advanced spark timing and stoichiometric mixture at full load.

This work presents a methodology for the optimal thermal management of different powertrain devices, with particular regard to ICEs, power electronic units (IGBT) and PEM Fuel cells. The methodology makes use of Model Predictive Control by means of a zero-dimensional model for the heat transfer between the device and the coolant. The control is based on the careful monitoring of the coolant thermal state by means of a metrics for the occurrence of nucleate boiling. The introduction of an electrically driven pump for the control of the coolant flow rate is considered. The effectiveness of the proposed approach is presented with reference to an ICE operation. Experimental tests show the advantages of the methodology during warm-up, under fully warmed operation and for the avoidance of after-boiling.

In this paper, we propose a novel control architecture for dealing with the requirements arising in a cooling system of an ICE. The idea is to take advantage of the joint action of an electric pump and of an ad-hoc regulation module, which is used to determine adequate flow rates despite engine speeds. Specifically, a robust Model Predictive Control approach is exploited to take care formally of input/output constraints and disturbance effects of the resulting lumped parameter model of the engine cooling system, which incorporates the nucleate boiling heat transfer regime. Numerical simulations and test rig experimental data are presented. The results achieved show that the proposed control scheme is capable of providing effective and safe cooling while mitigating disturbance effects and minimizing coolant flow rates when compared with the action pertaining to standard crankshaft driven pumps.

The aim of the present work is to analyse and compare the energetic performances and the emissions conversion capability of active and passive aftertreatment systems for lean burn engines. To this purpose, a computational one-dimensional transient model has been developed and validated. The code permits to assess the heat exchange between the solid and the exhaust gas, to evaluate the conversion of the main engine pollutants, and to estimate the energy effectiveness. The response of the systems to variations in engine operating conditions have been investigated considering standard emission test cycles. The analysis highlighted that the active flow control tends to increase the thermal inertia of the apparatus and then it appears more suitable to maintain higher temperature level and to guarantee higher pollutants conversion at low engine loads after long full load operation.

The present study aims at analyzing the flow field within a Lean NOx Trap (LNT). To this purpose a twofold approach based on the synergic use of numerical and non-intrusive experimental techniques was adopted. The measurements were carried out at a steady flow rig in terms of global performances and local velocity measurements. In particular, mass flow rates and pressure drops were used to define the global fluid dynamic efficiency of the system, while the Laser Doppler Anemometry (LDA) technique was employed to determine the flow field within the aftertreatment apparatus. At the same time, a finite volume CFD code was adopted for the numerical analysis. The comparison between experimental and numerical data displayed a good agreement in terms of global and local quantities. Specifically, the numerical code well-reproduced the main structure within the emission control system.

The work aims at analysing the energetic performances of monolith and pellet emission control systems using unidirectional and reverse-flow design (passive and active flow control respectively). To this purpose a one-dimensional transient model has been developed and the cooling process of different system configurations has been studied. The influence of the engine operating conditions on the system performances has been analysed and the fuel saving capability of the several arrangements has been investigated. The analysis showed that the system with active reverse flow and pellet packed bed design presents higher heat retention capability. Moreover, the numerical model put in evidence the large influence of the exhaust gas temperature on the energy efficiency of the emission control systems and the significant effect of unburned hydrocarbons concentration.

The development and the optimization of aftertreatment systems are fundamental keys to meet the more and more severe regulations concerning automotive exhaust emissions. This paper aims to analyse and compare the energetic performances of passive and active aftertreatment systems. The passive flow control represents the technical solution largely adopted in practice with unidirectional flow within the aftertreatment system. Conversely, the active flow control is based on reversed flow systems and, additionally, on the control of the exhaust gas flow path through the monolith. A single channel one-dimensional model was proposed in order to assess the heat exchange between the aftertreatment system and the exhaust gas and to compare the energetic characteristics of the two control modes. The analysis showed that the active flow control appears more suitable to maintain the initial temperature level of the monolith for a longer time after sudden variations in engine load.

The fluid dynamic behavior of four-valve high performance engines were investigated at the steady flow rig. In particular, the intake phase was considered. A global characterization was performed using the discharge coefficient, while the Laser Doppler Anemometry (LDA) technique was adopted to define the flow field around the intake valves. The purpose of the paper is to evaluate the influence of the valve-to-wall clearance on the flow distribution inside the combustion chamber. The analysis showed that, at low valve-to-wall distances, velocities (and therefore the engine volumetric efficiency) increase as the valves move away from the cylinder. The dependence is very strong for small distance values (lower than 2.5 mm) while it becomes weaker as the valve-wall clearance increases.