Particulate Formation in GDI Engines
Doktorsavhandling, 2022

The need to comply with stringent emission regulations while improving fuel economy and reducing criteria pollutant emissions from transportation presents a major challenge in the design of gasoline Direct Injection (DI) engines because of the adverse effects of ultrafine Particulate Number (PN) emissions on human health and other environmental concerns. With upcoming advances in vehicle electrification, it may be the case that electric vehicles completely replace all current vehicles powered by internal combustion engines ensuring zero emissions. In the meantime, Gasoline Direct Injection (GDI) engines have become the primary mode of transportation using gasoline as they offer better fuel economy while also providing low CO2 emissions. However, GDI engines tend to produce relatively high PN emissions when compared to conventional Port Fuel Injection (PFI) engines, largely because of challenges associated with in-cylinder liquid fuel injection. Cold-starts, transients, and high load operation generate a disproportionate share of PN
emissions from GDI engines over a certification cycle. The mechanisms of PN formation during these stages must therefore be understood to identify solutions that reduce overall PN emissions in order to comply with increasingly strict emissions standards.

This work presents experimental studies on particulate emissions from a naturally aspirated single cylinder metal gasoline engine run in a homogeneous configuration. The engine was adapted to enable operation in both DI and PFI modes. In PFI mode, injection was performed through a custom inlet manifold about 50 cm from the cylinder head to maximize the homogeneity of the fuel-air mixture. The metal head was eventually modified by incorporating an endoscope that made it possible to visualize the combustion process inside the cylinder. The experimental campaigns were structured to systematically isolate and clarify PN formation mechanisms. Tests were initially performed in steady state mode to obtain preliminary insights and to screen operating conditions before conducting transient tests. Particulate emissions were measured and correlated with the
images obtained through endoscope visualization where possible.

Key objectives of these studies were to find ways of reducing PN formation by increasing combustion stability. It was found that by avoiding conditions that cause wall wetting with liquid fuel, PN emissions can be substantially reduced during both steady state operation and transients. Warming the coolant and injecting fuel at later timings reduced PN emissions during warmup and cold transient conditions. Additionally, experiments using fuel blends with different oxygenate contents showed that the chemical composition of the fuel strongly influences particulate formation under steady state and transient conditions, and that this effect is load-dependent.

Overall, the results obtained in this work indicate that wall wetting is the dominant cause of particulate formation inside the cylinder and that fuel-wall interactions involving the piston, cylinder walls, and valves during fuel injection account for a significant proportion of PN emissions in the engine raw exhaust.

PM

Alternate fuels

Gasoline Direct Injection

internal combustion engines

Particulate Number

Load transients

EB, lecture hall, EDIT trappa C, D och H, Campus Johanneberg .
Opponent: Andre Boehman, professor, University of Michigan, USA

Författare

Sreelekha Etikyala

Chalmers, Mekanik och maritima vetenskaper, Förbränning och framdrivningssystem

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Not every technology that successfully impacts the lives and minds of one generation will carry it’s influence into the generations that follow. The widespread usage of internal combustion engines, especially in passenger cars argues strongly for gasoline’s ability to generate power instantaneously and efficiently in transportation. But it also reveals a hidden hunger in us to eagerly claim the technology and make it a part of our daily routines to embrace the benefits of low CO2 emissions and improved fuel consumption.

These properties distinguish gasoline direct injection (GDI) engines run with renewable fuels (without any infrastructure changes), from all other efforts towards sustainable transportation. Certainly, there are disadvantages with solely depending on liquid fuel combustion that cannot be ignored when it comes to public health and climate goals, especially particulate emissions. Most recent technical advances in electrification will benefit the world and public health by getting rid of tail-pipe emissions. While the complete transition to electric drive is underway, this thesis aims to provide knowledge on how GDI engines can wield the power to stay relevant and efficient in the coming decade by employing sustainable solutions that profoundly reduce particulate emissions.

This thesis investigates the potential in studying soot formation at a fundamental level through images and experiments that provide adequate resources to formulate data-driven control strategies for reduction of particulate number (PN) emissions. This research also focusses on how such data- driven solutions translates to GDI engines run with fuel blends, multiple injection strategies and even renewable fuels like E85. The conclusion is that in a field that changes as rapidly as transportation, GDI engines have the potential to serve the purpose of easy transportation with almost zero emissions with certain control strategies in the coming years. Nonetheless, this thesis aims to be a delta contribution to reducing the crisis of transportation related environmental and public health damage.

Ämneskategorier

Maskinteknik

Annan maskinteknik

Teknisk mekanik

Energiteknik

Strömningsmekanik och akustik

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Energi

Fundament

Grundläggande vetenskaper

ISBN

978-91-7905-745-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5211

Utgivare

Chalmers

EB, lecture hall, EDIT trappa C, D och H, Campus Johanneberg .

Online

Opponent: Andre Boehman, professor, University of Michigan, USA

Mer information

Senast uppdaterat

2023-11-08