EFFECT OF ELEVATED PISTON TEMPERATURE ON COMBUSTION CHAMBER DEPOSIT GROWTH

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EFFECT OF ELEVATED PISTON TEMPERATURE ON
COMBUSTION CHAMBER DEPOSIT GROWTH
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COMBUSTION CHAMBER DEPOSITS

• Combustion chamber deposits are recognized as a
  major contributor to the deterioration of SI
  engine performance
• Their build-up leads to increased charge
  emissions, and increased tendency for knock
• The factors influencing deposit formation are
  changes in fuel composition, coolant
  temperatures, engine speed and load, and spark
  timing

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EFFECT OF CCD

• The effect of combustion chamber deposits include
  octane requirement increase, decreased volumetric
  efficiency, combustion chamber deposit
  interference (CCDI)
• Combustion chamber deposit interference is the
  result of physical contact between deposits on
  the piston top and cylinder head
• combustion chamber deposits increases engine-out
  emissions of pollutants such as unburned
  hydrocarbons and nitric oxides

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EFFECT OF WALL TEMPERATURE ON CCD

• formation of fuel deposits is due to the
  condensation of components like aromatics
• With increased wall temperature hydrocarbon
  condensation decreases, deposit formation reduces

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PURPOSE OF THIS STUDY

• An experimental study was conducted to
  investigate the effect of elevated wall
  temperature on deposit growth
• This study monitors CCD growth as a function of
  metal wall temperature
• Attempts are made to determine critical wall
  temperature for no growth

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EXPERIMENTAL SETUPTEST ENGINE CONFIGURATION

• Performed on a single cylinder, variable
  compression ratio, cooperative fuel research
  engine
• The fuel delivery system was converted from the
  CFR system to a modern EFI setup
• Engine oil and water jacket cooling was provided
  by tube type heat exchanger
• Oil temperature in the crankcase sump was
  maintained at 902 ºC

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CONTROL MEASUREMENT OF PISTON SURFACE
TEMPERATURES

• A composite piston design was developed
• By varying the thickness of the ceramic wafer,
  the surface temperature of the cap could be
  increased

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THERMOCOUPLE LOCATION ON THE CAP
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TEST PROCEDURE

• The test schedule was broken down into four and
  one-half hour test cycles
• Within each test cycle a repeated fifteen minute
  test segment was conducted
• 1.5m-idle
• 13m-low load
• 0.5-high load

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MONITORING OF DEPOSIT GROWTH

• A technique for monitoring deposit growth is
  through the measurement of local surface
  temperature using thermocouples
• As deposit buildup on the surface, forms
  insulation barrier, reduces heat flow, reduces
  walls surface temperature
• Rate of change of wall surface temperature is
  indicative of rate of deposit growth

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TEST USING UNLEADED FUEL

• Caps insulated with 1,2 and3 mm ceramic wafers
  were tested with unleaded fuel
• Insulating the piston cap raised the initial
  temperature of the surface from an average of
  215C to 317C
• Elevating the initial temperature of the cap
  reduced its rate of decay with time
• -0.38C/hr (baseline) to -0.02C/hr (3 mm
  cap)

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COMPARISON OF SURFACE-AVERAGED WALL TEMPERATURES
OF BASELINE INSULATED CAPS
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TEST USING UNLEADED FUEL WITH REFORMER BOTTOMS

• The 3 mm cap test was repeated using unleaded
  fuel containing reformer bottoms
• Reformer bottoms are large hydrocarbon molecules
  having poor oxidation characteristics. It
  enhances deposit growth rate
• There is a linear decay in the average
  temperature of piston surface at a rate of
  0.35C/hr
• Reformer bottoms can promote deposit growth

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COMPARISON OF DECAY HISTORIES OF UNLEADED FUEL
WITH WITHOUT REFORMER BOTTOMS
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TEST ANALYSIS-PHYSICAL ANALYSIS

• At the end of baseline test(12hr)
• region 1,2 4-dark brown in color
• region 3-lighter shade of brown
• using 1 mm insulated cap
• average deposit thickness-6.28µm
• using 2 mm insulated cap-1.83µm
• using 3 mm insulated cap-negligible deposit
  
• 
  accumulation

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REGIONS WHERE MEASUREMENTS WERE TAKEN
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CORRELATION B/N AVERAGE PST AVERAGE DDEPOSIT
GROWTH

• The average deposit thickness was found to
  decrease at 3.38µm per mm of ceramic insulation

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CHEMICAL ANALYSIS

• According to test data, the deposits in the end
  gas region have highest fuel content. It is due
  to the deposition of unburned hydrocarbon
  products
• The region b/n sparkplug and intake valve have
  lower fuel content. This is due to fuel
  vaporization (16ºC more hotter)
• Deposits in the caps edge have highest oil
  content

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EFFECT OF WALL SURFACE TEMPERATURE ON C/H RATIO

• Increase in ST-decrease in concentration of
  carbon
• Increase in ST-decrease in C/H ratio
• Deposits on high temperature CC walls were
  composed of inorganic compounds

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CONCLUSION

• Elevating piston temperature critically affected
  deposit formation in SI engine combustion chamber
• No deposit growth was obtained when operating
  with a WST of 320C
• Test using unleaded fuel with reformer bottoms
  yielded a 55 increase in deposit growth
• Elevating WT, decrease C/H ratio of deposits

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