Grantee Research Project Results
1997 Progress Report: Combustion Chamber Deposit Effects on Engine Hydrocarbon Emissions
EPA Grant Number: R824970C002Subproject: this is subproject number 002 , established and managed by the Center Director under grant R824970
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (1989) - Northeast HSRC
Center Director: Sidhu, Sukh S.
Title: Combustion Chamber Deposit Effects on Engine Hydrocarbon Emissions
Investigators: Heywood, John B. , Hochgreb, Simone
Institution: Massachusetts Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1992 through June 30, 1997
Project Period Covered by this Report: January 1, 1996 through June 30, 1997
Project Amount: Refer to main center abstract for funding details.
RFA: Center on Airborne Organics (1993) Recipients Lists
Research Category: Targeted Research
Objective:
(1) To design a carefully-controlled experiment for deposit accumulation and HC emission measurement. (2) To assess the effects of combustion chamber deposits on the hydrocarbon emissions from a modern production spark-ignition engine. (3) To measure the effect of CCD on HC emissions from single-component fuels. (4) To develop and validate a model for the mechanism(s) by which combustion chamber deposits lead to additional HC emissions. (5) To study the effects of combustion chamber deposits on NOx emissions.Rationale: Engine deposits (on intake valve and combustion chamber) increase HC emissions. Some recent data suggest that combustion chamber deposits also increase NOx emissions. To meet stringent future emissions standards, the emissions due to deposits will have to be reduced. The first step towards that end is to better quantify these emissions and understand the mechanisms involved in their formation.
Approach: A four-cylinder, DOHC Saturn engine has been subjected to a standardized deposit build-up cycle. An additized fuel (which keeps the intake valves and ports clean) was used to isolate the effects of the combustion chamber deposits on emissions. HC and NOx emission measurements were taken continuously during the deposit accumulation process. In parallel a model for the effect of deposits on HC emissions has been developed.
Status: The project has now been completed. Four deposit build-up tests (100, 50, 25, and 35-hour tests) were carried out. In these tests, the HC emissions stabilized after about 25 hours. The HC emissions increased by an average of 14% due to deposit build-up. The HC emissions returned to the clean engine baseline levels after the combustion chamber deposits were removed. The NOx emissions, which were expected to increase slightly during these tests, showed substantial scatter and no clear trend was apparent.
The deposit accumulation process developed has shown that deposits can be built up systematically and reproducibly in engine dynamometer tests. The HC emissions trends were surprisingly repeatable. The significant finding was that the HC emissions increased for the first 20 hours of operation and then stabilized, even though deposits continued to build up. Thus engines will have to be very "clean" to largely eliminate this increase--an important practical issue. The NOx emission variability noted above is believed due to variability in the engines EGR system. Despite efforts to reduce this, no clear trends as deposits build up could be determined.
A model has been developed to explain the observed increase in HC emissions as deposits build up, and the lack of sensitivity of this increase to fuel compound in the individual hydrocarbon fueled tests. Critical to the development of this model were studies of the pore size distributions of the cylinder head and piston crown deposits (which had different characteristics).
Three different mechanisms were examined to explain the effect of CCDs on the HC emissions. The first is the displacement of fuel-air mixture into and out of the larger deposit pores as the cylinder pressure rises and falls. The second consists of pressure driven bulk flow into the deposit pores, in the pore size range (1 - 0.1 micrometer ) where viscosity is important. The deposits are treated as a porous medium with an estimated permeability. Darcy?s Law for flow in a porous medium forms the basis of this model. The third mechanism consists of ordinary diffusion of fuel molecules into the air (or exhaust gases) in the deposit pores. The fuel molecules diffuse into the deposit pores during the intake, compression, and combustion processes and get released into the combustion gases during the expansion and exhaust processes. During flow in, they are absorbed onto the pore surfaces. By applying these models to the appropriate pore size range, and weighting the trapped HC by the relative importance of these size ranges, the individual mechanism contributions to the total deposits impact was quantified. Only the crevice model of the larger (< 1 micrometer ) pores is significant, and the cylinder head deposits contribute many times what the piston deposits contribute. The model indicates that the pore depth to which fuel penetrates becomes limiting ( ~ 100 micrometer for the cylinder head) even though the deposit thickness steadily increases beyond that.
The maximum amount of HC trapped in the deposits is reduced by oxidation and retention in the cylinder. Allowing approximately for these effects produces estimates of the increase in engine HC emissions comparable to the measured increases.
Key Personnel
Graduate Student: Haissam Haidar
Supplemental Keywords:
RFA, Scientific Discipline, Air, Waste, particulate matter, Environmental Chemistry, Atmospheric Sciences, Incineration/Combustion, combustion byproducts, ambient aerosol, particulates, gas-phase transformation, combustion chamber, chemical characteristics, environmental chamber studies, ambient measurement methods, emissions measurement, combustion emissions, atmospheric transformation, emissions, chemical kinetics, atmospheric transport, hydrocarbons, combustion, engine deposits, kinetc models, combustion contaminants, spark ignition engine, chemical speciation samplingProgress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R824970 HSRC (1989) - Northeast HSRC Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R824970C001 Chemical Kinetic Modeling of Formation of Products of Incomplete Combustion
from Spark-ignition Engines
R824970C002 Combustion Chamber Deposit Effects on Engine Hydrocarbon Emissions
R824970C003 Atmospheric Transformation of Volatile Organic Compounds: Gas-Phase
Photooxidation and Gas-to-Particle Conversion
R824970C004 Mathematical Models of the Transport and Fate of Airborne Organics
R824970C005 Elementary Reaction Mechanism and Pathways for Atmospheric Reactions
of Aromatics - Benzene and Toluene
R824970C006 Simultaneous Removal of Soot and NOx from the Exhaust of Diesel Powered
Vehicles
R824970C007 Modeling Gas-Phase Chemistry and Heterogeneous Reaction of Polycyclic
Aromatic Compounds
R824970C008 Fundamental Study on High Temperature Chemistry of Oxygenated Hydrocarbons
as Alternate Motor Fuels and Additives
R824970C009 Markers for Emissions from Combustion Sources
R824970C010 Experimental Investigation of the Evolution of the Size and Composition Distribution of Atmospheric Organic Aerosols
R824970C011 Microengineered Mass Spectrometer for in-situ Measurement of Airborne
Contaminants
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
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- Original Abstract
125 publications for this center
89 journal articles for this center