Direct Injection Engines & Soot: What Does The Research Say?

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SHOdded

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That first presentation was pretty insightful.

I'll toss this in. It is also pretty interesting...

http://www.greencarcongress.com/2009/04/developing-ecoboost-20090429.html

This article, unless I misread it, indicates the 3.5 EB specifically (and like nearly all GDI engines) only utilizes stratified lean burn at cold operation. All other conditions prompt homogeneous charges.

Though, it is described as a transient phenomenon in the first presentation in the OP. There is likely quite a bit of soot formation under the onset of high load situations.

Of course, I'm still trying to figure out how the 3.5EB operates in a closed loop control feedback at all times, save for cold start. You'd think as a result there'd be fewer soot deposits.
 
Even though they show a pic at 6000 rpm, the range optimized for is 1,500 to 5,500 rpm (a bit short of WOT at 6,200 rpm).  But if the presentation is a good guide, always have a) a good strong battery, b) an appropriately low viscosity oil for cold start, and c) heaters for the catalysts to decrease cranking time and speed up that initial warmup nearly free of emissions. 

I know on my MFI NA Edge, it takes a mere minute or less with gentle driving from initial startup to reach 1000F or so on the catalysts.  Any idea how fast that happens on these EBs?

A quick primer on GDI engines:
http://www.aa1car.com/library/what_is_gasoline_direct_injection.htm
 
A pair of articles comparing GDI and PFI engines (deposits, fuel economy, soot, etc.) - Abstracts only:
http://papers.sae.org/1999-01-1498/
http://papers.sae.org/1999-01-1499/

Four 1998 Mitsubishi Carismas, two equipped with direct injection (GDI) and two with port fuel injection engines (PFI) were tested in a designed experiment to determine the effect of mileage accumulation cycle, engine type, fuel and lubricant type on engine wear and engine oil performance parameters. Fuel types were represented by an unadditised base fuel meeting EEC year 2000 specifications and the same base fuel plus synthetic deposit control additive packages. Crankcase oils were represented by two types (1) a 5W-30 API SJ/ILSAC GF-2 type engine oil and (2) a 10W-40 API SH/CF ACEA A3/ B3-96 engine oil.

The program showed that engine fuel system deposits, including specifically those on intake valves, combustion chambers and injectors are formed in higher amounts in the GDI engine than the PFI engine. The fuel additive used reduced injector deposits and combustion chamber deposits in the GDI, but had no significant effect on intake valve deposits, which are affected by crankcase oil formulation. In GDI vehicles, deposited engines were found to have increased hydrocarbon and carbon monoxide emissions and poorer fuel economy and acceleration, but lower particulate emissions. Effects in PFI engines were directionally the same for NOx and particulates but the opposite for HC and CO emissions and fuel economy. In terms of specific deposit effects in the GDI engine, CCD is correlated with poorer acceleration, HC and CO emissions, while injector deposits correlate with NOX formation.

The program showed that specific selection of oil additive chemistry may reduce formation of intake valve deposits in GDI cars.. In general, G-DI engines produced more soot and more pentane insolubles and were found to be more prone to what appears to be soot induced wear than PFI engines. Again, proper selection of oil additive chemistry provided sufficient engine durability protection in both types of engines.
 
Advanced Particulate Filter Technologies for Direct Injection Gasoline Engine Applications
http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2012/wednesday/presentations/deer12_bischof.pdf

  • Continuing efforts for further CO2 and PN reduction create a challenging environment for vehicles equipped with DI gasoline engines
  • Gasoline particulate filters will be an enabler to meet these challenging targets either as an alternative or as a supplement to improved combustion recipes
  • Gasoline particulate filters can be designed:
                – As an “add on” solution to an existing after treatment system
                – As a gasoline particulate filter with integrated three way catalyst functionality
  • Optimized designs for gasoline particulate filter applications
 
In-cylinder soot imaging and emissions of stratified combustion in a spark-ignited spray-guided direct-injection gasoline engine
http://www.scopus.com/record/display.url?eid=2-s2.0-84858215701&origin=inward&txGid=CEDEAE0A0F62CC8BEF6CE4D1D18B0D5C.fM4vPBipdL1BpirDq5Cw%3a2

... the engine-out soot emission measurements, which showed increased soot levels as the injection was retarded. It was also found that fuel impinged on the spark plug during the injections, resulting in a persistent jet flame close to the spark plug in the centre of the cylinder, which is believed to contribute to engine-out soot emissions ...
 
Numerical Investigation of Soot Formation in Gasoline Direct Injection Engines (2014)
http://www.ansys.com//staticassets/ANSYS/staticassets/resourcelibrary/presentation/aswc2014-soot-formation-direct-injection-engine.pdf

Summary
  • Liquid fuel films are emitted as one of followings
          – remaining fuel films
          – unburned hydrocarbons
          – precursors (C2H2, PAHs..)
          - soot
  • Emission factors of UHC and soot can be expressed as a function of the wall temperature
  • A surface reaction mechanism including pyrene and coronene as precursors was constructed based on the literature
  • Particle number emissions generated from combustion of liquid fuel films during cold startup period were estimated by using the method of moments
 
Could we be sucking in cleaner air in the cooler months with the dirty exaust vapors being warmer and their natural tendency is to rise? My simple minded thought on the absence of soot from my unchanged setup.

Rich

 
GDI engines s(n)oot-ier than diesel?

Vehicle tests show that without the use of gasoline particulate filters (GPF), more particles are emitted from gasoline direct injection (GDI) engines than diesels. On the road, GDI vehicles may therefore exceed future European emissions limits – the Euro 6 standard. The cost of a filter to eliminate particle emissions is low (around €50), with no fuel economy penalty. Despite this, carmakers are declining to fit filters to GDI cars – thereby worsening urban air pollution. T&E calls upon carmakers to ensure GDI cars minimize their particle emissions by fitting filters. Carmakers should not use unreliable ‘engine management’ approaches to try and control emissions, as these produce much higher numbers of particles, particularly during on-road driving.

http://www.transportenvironment.org/sites/te/files/publications/GDI%20Briefing_final_T%26E.pdf
 
Experimental and Numerical Investigation of the Idle Operating Engine Condition for a GDI Engine

http://www.academia.edu/1282134/Combustion_process_analysis_for_a_GDI_engine_in_the_idle_operating_engine_condition_during_the_warm-up

Abstract:

The increased limitations to both NOx and soot emissions have pushed engine researchers to rediscover gasoline engines. Among the many technologies and strategies, gasoline direct injection plays a key-role for improving fuel economy and engine performance. The paper aims to investigate an extremely complex task such as the idle operating engine condition when the engine runs at very low engine speeds and low engine loads and during the warm-up. Due to the low injection pressure and to the null contribution of the turbocharger, the engine condition is far from the standard points of investigation. Taking into account the warm-up engine condition, the analyses are performed with a temperature of the coolant of 50°C.

The paper reports part of a combined numerical and experimental synergic activity aiming at the understanding of the physics of spray/wall interaction within the combustion chamber and particular care is used for air/fuel mixing and the combustion process analyses. In order to properly describe the engine condition, different injection strategies are investigated. Late and early injection strategies are deeply analyzed and compared in terms of combustion stability and pollutant emissions.

UV-visible imaging and spectral measurements are carried out in real engine with wide optical accesses... Measurements are performed in the optically accessible combustion chamber realized by modifying a real engine. The cylinder head was modified in order to allow in the fourth cylinder the visualization of the fuel injection and the combustion process with high spatial and temporal resolution.

The 3D-CFD engine simulations are reproduced by means the commercial code Star-CD. Due to the warm-up condition and the many physical sub-models a numerical methodology is implemented and particular care is used to boundaries conditions analyses. CFD analysis is used to find a possible explanation of the high cycle to cycle variability. The experimental and numerical comparisons, in terms fuel mixing and front flame propagation, give an explanation of the idle condition.

Publisher: papers.sae.org

Publication Date: Jan 1, 2012
 
Lean Burn Technology in GDI engines

http://www.autozine.org/technical_school/engine/petrol1.htm

Lean Burn Engine
Basically, engines which can operate in very lean air / fuel mixture are called "Lean Burn Engines". Japanese car makers, heading by Toyota, are the leaders in this technology.
Apparently, the leaner air / fuel mixture, the more frugal the engine is. But there are two reasons prevent conventional engines from operating in lean air / fuel mixture: 
[list type=decimal]
[*]If the mixture is too lean, the engine will fail to combust.
[*]Naturally, lower fuel concentration leads to less output.
[/list]
Lean burn engines avoid these problems by adopting a highly efficient mixing process. They use special shape pistons, with intake manifolds located and angled matching the pistons, the intake air will generate swirl inside the combustion chamber. Swirl leads to more complete mixing of fuel and air, thus largely reduce the badly-mixed fuel particles, which will not be burnt in conventional engines. This enables more complete burning, not only reduces pollutant, but also allow the fuel / air ratio to be lowered from 1 : 14 to 1 : 25 without altering output.

Today, Lean Burn technology has evolved into Direct Injection, which is basically the former added with direct fuel injection. Toyota, Mitsubishi and Nissan all concentrate in DI engines development.
 
Particle and metal emissions of diesel and gasoline engines - Are particle filters appropriate measures?
http://www.exisab.com/Docs/Conferences/ETH_Nanoparticle_2012/Ulrich.pdf

Emissions of metal oxide particles can occur for all types of internal combustion engines. Even if clean fuels are used,
lubrication oil remains as a potential source for metal oxide particles. Full-wall-flow particle filter systems have shown
high filtration efficiency in diesel exhaust gas after-treatment. However, this study demonstrated that they can be also
useful to remove metal oxide emissions from other engine types. An effective filtration of metal particles is important to
reduce toxic potential of nanosized particles and metals. Hence, filtration technology is promising not only for diesel
engines (soot filtration) but for all types of combustion engines. The filtration efficiency for metals should be further
investigated in future projects.
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