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Technical Paper

Experimental Analysis of the After-Boiling Phenomenon in a Small I.C.E.

An experimental investigation was conducted on a production 4-cylinder, MPI small S.I. engine, 1.2 dm3 displacement, which was operated at 4000 rpm full load, then brought to idle for a short period and finally switched off. As the coolant flow stops while the metal temperature is quite high, a fraction of coolant vaporizes, pressure and temperature increase and part of the coolant is lost through the radiator pressure relief valve. This phenomenon is often known as after-boiling. Tests were carried out for different values of the idle operation time, while coolant conditions and metal temperature at 26 points of the engine head and liner were monitored for 2 mins before and 15 mins after engine switch-off. The volume of leaked coolant as well as the start and finish of the expulsion process were also recorded.
Journal Article

A Novel Cooling System Control Strategy for Internal Combustion Engines

An innovative control strategy, which is based on the Robust Model Predictive Control (MPC) methodology, was developed with the purpose of optimizing the engine thermal management; the proposed control strategy adjusts the coolant flow rate by means of an electric pump, in order to bring the cooling system to operate around the onset of nucleate boiling. In the present paper, the advantages of the proposed cooling approach are evaluated along the NEDC homologation cycle, which was both simulated and replicated by means of laboratory tests; the latter include coolant, lubricant and wall temperature measurements. Special attention was reserved to the warm-up period. The case considered herein is that of a Spark Ignition engine, about 1.2 dm3 displacement, and a comparison with standard crankshaft driven pump is included.
Technical Paper

Knock Mitigation by Means of Coolant Control

The possibility to mitigate the knock onset by means of a controlled coolant flow rate is investigated. The study is carried out on a small displacement, N.A. 4-valve per cylinder SI engine. The substitution of the standard belt-driven pump with an electrically driven one allows the variation of the coolant flow rate regardless of engine speed and permits, therefore, the adoption of a controlled coolant flow rate. The first set of experimental tests aims at evaluating the engine operating condition and the coolant flow rate, which are more favorable to the knock onset. Starting from this condition, subsequent experimental tests are carried out for transient engine operating conditions, by varying the coolant flow rates and evaluating, therefore, its effects on cylinder pressure fluctuations. In all the experiments, the spark advance and the equivalence ratio are controlled by the ECU according to the production engine map.
Technical Paper

ICE Thermal Management: A Model Predictive Control Approach for CO2 Reduction

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.
Technical Paper

A Model Predictive Approach to Avoid Coolant After-Boiling in ICE

The after-boiling phenomenon in internal combustion engines can occur when the engine is suddenly switched-off after a period of prolonged high-load operation. In this case, the coolant flow rate stops while the engine wall temperature is quite high; therefore, some evaporation occurs, pressure in the cooling circuit increases and part of the coolant is lost through the radiator relief valve. The control of the coolant flow rate by means of an electric pump instead of the standard belt driven one offers the possibility of overcoming this issue. In the present paper, a model-based control of the coolant flow rate is proposed in conjunction with the adoption of an electric pump in the engine cooling system. Experimental tests and simulations have been carried out starting from high speed-high load engine operation; the engine was then brought to idle and, shortly after, switched-off.
Technical Paper

Powertrain Thermal Management for CO2 Reduction

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.
Technical Paper

A Zero-Dimensional Two-Phase Model of the Thermal Transient of an I.C.E. Cooling System after a Rapid Switch-off

The paper illustrates a zero-dimensional dynamic model which was developed in the MATLAB®/Simulink environment to predict thermal transient of an automotive cooling system. In particular, the rapid switch-off of an internal combustion engine which was operated for a prolonged time at high speed under full load was investigated. In this condition, significant vapour formation and, consequently, pressure rise within the cooling circuit can arise, because of the sudden heat transfer from the high temperature head metal to the coolant contained in the cylinder head passages. The proposed model allows predictions of the vaporized mass of coolant as well as of the pressure evolution within the cooling circuit. The simulations results were compared with experimental tests carried out on a production 4-cylinder, MPI small S.I. engine, 1.2 dm3 displacement, and the agreement was very satisfactory.