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Water injection is one of the most promising technologies to improve the engine combustion efficiency, by mitigating knock occurrences and controlling exhaust gas temperature before turbine. As result, the engine can operate at stoichiometric conditions over the whole engine map, even during the more power-demanding RDE cycles. Antonino Vacca presents a methodology to study and optimize the effect of water injection for gasoline engines by investigating different engine layouts and injection strategies through the set-up of a 3D-CFD virtual test bench. He investigates indirect and direct water injection strategies to increase the engine knock limit and to reduce exhaust gas temperature for several operating points.

### Chapter 1. Introduction

Abstract
Today water injection is investigated for turbocharged gasoline engines to improve engine efficiency over the whole operating range [28]. Several studies on the effect of ethanol-fuel and water demonstrated how to lower down the intake temperature and to decrease the Knock sensitivity. The reason is essentially their higher heat of vaporization (HOV) and particularly water with respect to commercial gasoline [15].
Antonino Vacca

### Chapter 2. Fundamentals of CFD for ICEs

Abstract
The majority of current ICEs are no longer naturally aspirated, instead they employ boost systems to increase the air density. Usually, this is realizes via a turbomachine and particularly with a turbocharger, which exploits exhaust gas enthalpy to compress fresh air and to raise the engine volumetric efficiency. The objective is to suck as much air as possible decreasing engine displacements while keeping the same rated power. This practice is generally known as engine downsizing.
Antonino Vacca

### Chapter 3. The 3D-CFD Virtual Test Bench

Abstract
This chapter provides an overview of the CFD methodology used in the current work. Starting from the equations presented in chapter 2, the classical CFD approach is extended towards a time-effective analysis dedicated expressly to the development of internal combustion engine (see also chapter 1.3). This analysis is marked out as 3D-CFD Virtual Test Bench because of the massive amount of configurations tested through simulations and for the similarity to the experimental methodology usually adopted for the investigation of the engine thermodynamics at the test bench.
Antonino Vacca

### Chapter 4. Simulation of Injections

Abstract
Beyond the implementation of water physics in QuickSim, further development of the injection model was accomplished. The improvements of the injection model were realized by coupling optical measurements performed in a constant volume chamber and by the setting of a new methodology to calibrate the simulations with a repeatable analysis of both experimental and numerical results. Axial and radial penetration curves, injection tip velocity, as well as jet angles, were measured and evaluated. The injection model calibration realized through these data, enhance the simulations’ reliability.
Antonino Vacca

### Chapter 5. Optimization of the Engine Map through Water Injection

Abstract
The current chapter provides a description of the experimental and simulation methodology, especially with a focus on the investigation of the thermodynamics of a single-cylinder engine whose date will be resumed in the next section (chapter 5.1).
Antonino Vacca

### Chapter 6. Water Injection for Enhancing Knock Resistance

Abstract
As mentioned in chapter 5, OP1 (2000 rpm, 20 bar IMEP) presented a marked tendency to knocking combustion. Therefore the spark advance for OP1 was set to 1 °CA b.FTDC in the base engine calibration. Considering OP1, in the following analysis different parameters were varied, and their combination tested, to find the most promising strategies for the rise of the engine indicated efficiency while limiting at the same time water consumption.
Antonino Vacca

### Chapter 7. Influence of Water Injection on Soot Formation

Abstract
The current chapter reports an extract of the paper [21] and particularly the influence of water injection timing on the soot production, both considering experiments and 3D-CFD simulations. The emission investigations have been led at OP2, the only considered load point that did not present constraints neither in terms of Knock onset nor considering exhaust gas temperature before turbine. For such reasons the water injection potentials are investigate on OP2 not with the purpose of increasing the engine efficiency, but for evaluate the effects in terms of emission reduction.
Antonino Vacca

### Chapter 8. Water Injection for Exhaust Gas Temperature Control

Abstract
This chapter deals with the investigation of OP3, corresponding to rated power (4500 rpm 20, bar IMEP), generally critical for exhaust gas temperature management. Since executing this load point at the test bench was very critical for problems related to the cooling of the cylinder head, the entire analysis was conducted by exploiting the potential of the Virtual test bench.
Antonino Vacca

### Chapter 9. Conclusion and Outlook

Abstract
Among others, water injection is one of the most promising technologies to improve the engine combustion efficiency, by reducing Knock occurrences, controlling exhaust gas temperature and allowing the engine operating at $$\lambda$$ =1 over the whole engine map.
Antonino Vacca