Enabling Lean and Stoichiometric Gasoline Direct Injection Engines through Mitigation of Nanoparticle Emissions

PI: Will Northrop, CO-PI: David Kittelson

Joonho Jeon, postdoctoral researcher, "Cyclic Variability of In-Cylinder Flame Luminosity in Gasoline Direct Injection Engines"

Noah Bock, PhD student, Thesis title: "Oxidative Reactivity of Nanoparticles Emitted from a Gasoline Direct Injection Engine"

Utilization of gasoline direct injection (GDI) technology for light duty vehicle applications has drastically increased in recent years due to the improved fuel efficiency relative to port fuel injection (PFI) technology. GDI technology also provides the option of fuel lean operation, which further increases efficiency. However, because GDI engines emit much higher concentrations of particulate matter (PM), their proliferation is in conflict with increasingly stringent PM limits. The use of gasoline particulate filters (GPFs) is expected to be largely adopted for use in GDI vehicles to meet PM limits. The question of how particle emissions from GDI engines are affected by fuel properties, oil additives, and engine combustion strategies must be answered to design engines that can meet both fuel efficiency goals and PM limits. Additionally, questions regarding the oxidative reactivity of GDI soot particles must be answered for the implementation of GPFs.

Sampling system and instrumentation from HTO-TDMA and TGA experiments

We are using advanced particle measurement instruments and techniques to examine particle formation phenomena in a BMW GDI test engine. The test engine has been fitted with an AVL Visiolution optical sensor (Visio sensor) that measures spatiotemporal flame luminosity in the combustion chamber. The Visio sensor is a probe that is inserted into the combustion chamber through a bore machined in the cylinder head. The tip of the probe contains three arrays of optical fibers with each array containing eight individual fiber optic channels that view different sections of the combustion chamber. Soot-producing diffusion flames emit light due to the incandescence of soot. Because of this, regions of high light intensity during the combustion process indicate areas of soot formation. The Visio sensor measures the location within the cylinder and at what point during the combustion process high light intensity occurs, and from this information, the origin and cause of the soot formation can be determined. The Visio sensor coupled with suspended particle measurement instruments gives us a wealth of information about how particles are formed in the engine, which can allow us to make changes to engine parameters to reduce the incidence of particle inception in the first place. We are also characterizing the performance of a three-way catalyst (TWC) wash coated GPF, sometimes referred to as a four-way catalyst (4WC), to determine the particle size resolved filtration efficiency. We are determining the oxidative reactivity of soot produced from a GDI engines and how it is affected by combustion strategy, fuel properties, and lubrication oil additives. This is critical for GPF implementation as it is a fundamental factor for determining soot loading on the filter, and the oxidation kinetics of soot for removal of soot from the filter through regeneration.

Soot particles emitted from internal combustion (IC) engines are formed in the combustion chamber from locally rich fuel/air regions. This can be caused by fuel wetting of cylinder surfaces, rich pockets of fuel vapor that has not mixed fully with the intake air, or liquid fuel droplets suspended in the intake charge that survive evaporation prior to combustion. These processes are strongly affected by fuel properties that influence evaporation characteristics, e.g. heat of vaporization and volatility. Additionally, fuel chemistry plays an important role in soot production. Aromatic compounds have a high propensity for soot formation. These effects have recently been studied for stoichiometric GDI operation. However, they have not been studied for lean GDI combustion strategies, which utilize late injection and fuel stratification that results in distinct particle size distributions. This can be attributed to the differences in formation environment of each respective strategy.

Publications

Solid Particle Number and Mass Emissions from Lean and Stoichiometric Gasoline Direct Injection Engine Operation

Sponsors:

Department of Energy

BP (In-Kind)

Fiat Chrysler Automobiles (In-Kind)