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Published on November 16, 2007

Author: Oceane

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Slide1:  DIRECT-FUEL-INJECTION GASOLINE ENGINES Arun Solomon General Motors R & D and Planning Powertrain Systems Research Laboratory Michigan State University College of Engineering ME 444 – Fall 2007 OUTLINE:  OUTLINE Historic evolution of fuel delivery systems for gasoline engines Direct-fuel-injection - benefits Past direct-injection stratified-charge (DISC) engine programs Why revisit the DISC engine? The modern gasoline direct-injection engine Summary and conclusions Gasoline-Engine Fuel Delivery Systems:  Gasoline-Engine Fuel Delivery Systems 1900 1985 Carburetor 1980 1995 Single-Point, Throttle-Body Fuel Injection 1980 ???? Multi-Port-Fuel-Injection 1995 ???? Advanced Multi-Port-Fuel-Injection 1996 ???? Direct (In-Cylinder) Fuel-Injection Slide4:  Carburetor Port-Fuel-Injection Direct-Injection Slide5:  A Typical Reverse-Tumble Wall-Controlled Direct-Injection Gasoline Engine Vertical Intake Ports that Generate Reverse-Tumble AirFlow Direct-Fuel Injector Spark Plug Piston with Bowl to Aid in Creation of Suitable Fuel-Air Mixture Historic Evolution of Gasoline-Engine Fuel Delivery Systems:  Historic Evolution of Gasoline-Engine Fuel Delivery Systems The evolution of gasoline-engine fuel delivery systems has been dictated by the need to improve transient and cold engine performance and emissions. With each evolutionary change in the fuel delivery system, air-fuel mixture preparedness, within the cylinder, had to be engineered and restored to the traditionally acceptable homogeneous state. Gasoline-Engine Fuel Delivery Systems:  Gasoline-Engine Fuel Delivery Systems Fuel System Carburetor Single-Point, Throttle-Body Fuel Injection Multi-Port- Fuel-Injection Advanced Multi-Port- Fuel-Injection Direct-Fuel- Injection Transient Emissions & Control * * * * * * * * * * * * * * * Cold Emissions & Control * * * * * * * * * * * * * * * Mixture Preparation Quality * * * * * * * * * * * * * * * * Cost & Complexity * * * * * * * * * * * * * * * Slide8:  Will direct-fuel-injection replace electronic port-fuel-injection at a similar rate? Direct-Fuel-Injection - Preliminary Goal:  Direct-Fuel-Injection - Preliminary Goal Preliminary goal for a Direct-Fuel-Injection system is therefore to be able to achieve the traditionally acceptable homogeneous air-fuel mixture state at the time of ignition, by: Promoting maximum air-fuel mixing Using a finely atomized spray Prevent wall wetting Injecting early during intake stroke Intake-port design Injector location Direct-Fuel-Injection - Benefits:  Direct-Fuel-Injection - Benefits However, because of the big increase in cost and complexity of a DFI system, would like to get more benefits to offset system costs than just improved cold and transient engine performance and emissions. Are there any additional benefits of a DFI system? Yes. Increased Fuel Economy !! But, this increase in thermal efficiency is currently possible only if the mixture-preparation state, within the cylinder, is stratified and not the traditionally acceptable homogeneous state. DI Gasoline Fuel Economy & Emissions (First Order Benefits and Risks) :  DI Gasoline Fuel Economy & Emissions (First Order Benefits and Risks) Mixed Mode Likely Operating Range Emissions Risk Fuel Economy Expect Reduced Cold and Transient Emissions Homogeneous Charge (Throttled) Stratified Charge (Unthrottled) Needs In-Cylinder NOx and HC Control Needs Lean NOx Catalyst Thermodynamic Levers to Increase Thermal Efficiency:  Thermodynamic Levers to Increase Thermal Efficiency Increased volumetric efficiency increased compression ratio Decreased throttling losses Lean combustion Decreased heat losses In trying to work the above levers, DFI is an enabler with high potential. Note that advanced MPFI systems are also enablers, but with lesser potential than DFI. Direct-Fuel-Injection – Benefits Increased Volumetric Efficiency:  Direct-Fuel-Injection – Benefits Increased Volumetric Efficiency Direct-Fuel-Injection – Benefits Increased Volumetric Efficiency:  Direct-Fuel-Injection – Benefits Increased Volumetric Efficiency Direct-Fuel-Injection can result in an increase (up to 8% has been reported) in airflow due to spray-cooling of the intake air, when injection occurs during the intake stroke. The resulting increased performance can be converted to 1-2% increase in fuel economy. Direct-Fuel-Injection – Benefits Increased Compression Ratio :  Direct-Fuel-Injection – Benefits Increased Compression Ratio Note: Otto-Cycle efficiency is used as a gross approximation for illustrative purposes Direct-Fuel-Injection – Benefits Increased Compression Ratio :  Direct-Fuel-Injection – Benefits Increased Compression Ratio Direct-Fuel-Injection – Benefits Increased Compression Ratio :  Direct-Fuel-Injection – Benefits Increased Compression Ratio Direct-Fuel-Injection permits an increase in compression ratio from 10.5 to about 12.0, resulting in about 2% increased efficiency. The increase in compression ratio results from a higher knock-tolerance (I.e., higher knock-limited spark advance) due to: 1. Spray cooling of the intake air when injection occurs during the intake stroke 2. Reduced end-gas temperature when injection occurs during compression stroke Direct-Fuel-Injection – Benefits Decreased Throttling Losses :  Direct-Fuel-Injection – Benefits Decreased Throttling Losses Throttling losses are reduced by diluting the mixture with EGR or with excess air. But in a conventional homogeneous-charge system, the extent of dilution is limited due to flame initiation and propagation limits. By stratifying the fuel-air mixture within the combustion chamber, the engine can be operated with extended dilution, at air-fuel ratios of 50:1 or greater. Slide19:  Ideal Throttling Loss Effects on Net Thermal Efficiency (%) Slide20:  Ln Volume Ln Pressure Diluting the Air-Fuel Mixture Reduces Pumping (or Throttling) Losses Undiluted Combustion Partially Diluted Combustion (Partially Unthrottled) Fully Diluted Combustion (Fully Unthrottled) IMEP PMEP Net MEP = IMEP - PMEP Reduced Pumping Loss Due to Dilution IMEP IMEP PMEP Direct-Fuel-Injection – Benefits Lean Combustion:  Direct-Fuel-Injection – Benefits Lean Combustion Note: Otto-Cycle efficiency is used as a gross approximation for illustrative purposes Direct-Fuel-Injection – Benefits Lean Combustion:  Direct-Fuel-Injection – Benefits Lean Combustion When the working fluid has a higher specific-heat ratio like that of lean air-fuel mixtures, less fuel energy is wasted in raising the internal energy of the charge, so more is available for useful work. By stratifying the fuel-air mixture within the combustion chamber, the engine can be operated at very lean (up to 50:1) air fuel ratios. Direct-Fuel-Injection – Benefits Decreased Heat Losses :  Direct-Fuel-Injection – Benefits Decreased Heat Losses By stratifying the fuel-air mixture in the center of the combustion chamber and keeping the hot burnt products away from the walls, heat losses can be decreased. Slide24:  Idealized Unthrottled Stratified-Charge Operation Idle Mid-Load High-Load Air or (Air + EGR) (Fuel+Air) or (Fuel+Air+EGR) AF = 18-20 Ln Volume Ln Pressure Idealized Unthrottled Stratified-Charge Operation :  Idealized Unthrottled Stratified-Charge Operation Fuel Economy (Relatively Easier to Demonstrate) Little or no throttling losses (no pumping loop) Reduced heat losses (burning occurs with less contact with walls; overall temperature lower) Lean combustion (less heat used up in raising internal energy of charge so more available for useful work) Higher compression ratio (more knock tolerant because end-gas properties are favorably modified reduced thermal dissociation) Idealized Unthrottled Stratified-Charge Operation :  Idealized Unthrottled Stratified-Charge Operation Emissions (High Risk) Ideal properties of fuel-air cloud are difficult to attain, especially over entire load range Excessive lean fringes of cloud extinguish to cause a HC emissions problem Excessive stoichiometric regions of cloud cause NOx emissions problem Lean nature of combustion prevents use of a conventional 3-way catalyst (and lean-NOx catalysts still under development)) Slide27:  Some Major DISC-Engine Programs of the Past U.S. Army/Texaco - Texaco controlled combustion system (TCCS) Ford’s programmed combustion (PROCO) engine (1970’s) GM’s direct-injection stratified-charge (DISC) engine (1980’s) UPS-Texaco controlled combustion system (TCCS) Volkswagen gasoline direct injection (GDI) M.A.N. FM combustion engine Some Other DISC-Engine Programs and Activities of the Past:  Some Other DISC-Engine Programs and Activities of the Past Engine Manufacturers White, Porsche (SKS-engine), Deutz (AD combustion process), Honda, International Harvester, Curtiss-Wright U.S. Government U.S. Army/TACOM, EPA, DOE U.S. National Labs Sandia, Los Alamos, Lawrence Livermore, NASA Lewis Universities Princeton, MIT, Wisconsin, Michigan State, Imperial College, Aachen-Germany Consulting Houses SwRI, Ricardo Past DISC-Engine Programs - General Results:  Past DISC-Engine Programs - General Results Late Injection Fuel is injected relatively late in the compression stroke, ignition occurs during the injection process, and mixing of fuel and air occurs during and after ignition; permits relatively high compression ratio. High thermal efficiency (30% gain), good multi-fuel capability and excellent cold-start performance was demonstrated. Problems were encountered with high light-load hydrocarbon emissions, high mid-load nitric-oxide emissions, high-load particulates, combustion variability and specific power. Past DISC-Engine Programs - General Results:  Past DISC-Engine Programs - General Results Early Injection Fuel injection occurs relatively early in the compression stroke; major mixing between fuel and air takes place before ignition; compression ratio is more knock-limited like conventional homogeneous-charge SI engines. Expected gains in thermal efficiency were mostly realized. However, problems with high light-load hydrocarbon emissions, high mid-load nitric-oxide emissions and maximum power were encountered. A Simple Summary of the HC/NOx Problem:  A Simple Summary of the HC/NOx Problem Hydrocarbons: Major source of engine-out hydrocarbon emissions is due to quenching of the flame in the overly lean fringes of the fuel-air cloud. Nitric-oxide: Major source of engine-out nitric-oxide emissions is stoichiometric combustion at local regions, within the combustion chamber. Slide32:  A Simple Summary of the HC/NOx Problem Air or (Air + EGR) Stoichiometric AF = 14.6 Source of NOx Emissions Injector Spark Plug Too Lean AF > 40 Source of HC Emissions Rich AF < 14.6 Lessons from the Past:  Lessons from the Past Yes, unthrottled, direct-injected, stratified-charge operation of a gasoline spark-ignited engine yields significant gains in thermal efficiency. This gain comes from a reduction or elimination of throttling losses, increased compression ratio and lean combustion. But, the challenge for the stratified-charge engine is meeting future Federal and California hydrocarbon and nitric oxide emissions standards. This is due to high hydrocarbon emissions at light-loads and high nitric-oxide emissions at mid-load. Why Revisit the DISC Engine?:  Why Revisit the DISC Engine? Fuel Economy Eliminating Throttling Losses - Throttling losses still represent the largest single recoverable loss for the SI gasoline engine. Direct-Injection Gasoline Fuel Systems - Better DI fuel systems and large number of fuel-system suppliers are available due to efforts on DI two-stroke engine programs. Lean NOx Catalyst - Required for DISC; efficiency of these catalysts are constantly increasing. Why Revisit the DISC Engine?, continued:  Why Revisit the DISC Engine?, continued Engine Control Systems - Complex control systems needed for control of complex DISC combustion process are already here. Improved Understanding of Combustion Process - This is attributable to ongoing work and progress in understanding port-injected lean-burn, and direct-injected two-stroke and four-stroke combustion processes. Slide36:  JAPAN 1996 EUROPE 1998 US 200X ?? PROGRESSION OF OEM INTRODUCTIONS The Modern DFI Gasoline Engine Slide37:  Direct-Injection Combustion System Alternatives Homogeneous (Throttled) Mixed-Mode Stratified (Unthrottled) Charge-Motion Controlled (VW) Wall-Controlled Spray-Jet Controlled Tumble Wall-Controlled (Mitsubishi) Swirl Wall-Controlled (Toyota) Spray-Jet Controlled The Modern DFI Gasoline Engine Slide38:  CHARGE-MOTION CONTROLLED Dominated by interaction of bulk airflow with spray ADVANTAGES: Combustion rate scales better with engine speed Combustion control over load-range is easier DISADVANTAGES: Optimization over speed and load range is challenging, since spray is real-time event Potential for highly stratified operation may be limited Slide39:  WALL CONTROLLED Dominated by interaction of spray with wall ADVANTAGES: Light-load stratification easier to achieve Combustion is less sensitive to spray characteristics DISADVANTAGES: Wall-wetting during cold and heavy-load operation causes HC emissions and smoke Combustion modes are different in light-load and heavy-load regimes Slide40:  SPRAY-JET (or PUFF) CONTROLLED Dominated by spray characteristics ADVANTAGES: Potential for highly stratified operation DISADVANTAGES: Current sprays are not ideal (therefore usually requires deep bowl in piston for containment) Requires spraying directly onto spark-plug electrodes (therefore reduced plug durability) The Modern DFI Gasoline Engine :  The Modern DFI Gasoline Engine SAE 940483 (Ricardo/Isuzu) Siemens fuel injector (droplet size 5 to 10 microns) Operated direct-injected engine, with injection timings during intake stroke (homogeneous-charge), and obtained NOx, CO, HC emissions and fuel consumption competitive, with port-fuel-injected version of the same engine. Cold transient tests demonstrated that a direct-injected combustion system has the potential to operate without fuel enrichment during cold starts. The Modern DFI Gasoline Engine:  The Modern DFI Gasoline Engine Advances in direct-injection gasoline fuel systems and injectors enables the DI gasoline (homogeneous-charge) engine to have the potential of having lower emissions during cold and transient operation. The Modern DFI Gasoline Engine :  The Modern DFI Gasoline Engine SAE 940675 (Hokkaido U./Japan Railway Co.) Direct-injected stratified-charge operation with two-stage fuel injection. First stage fuel injection occurs before compression stroke to create uniform premixed lean mixture; second stage occurs at the end of the compression stroke to maintain stable ignition and faster combustion. 30% reduction in fuel consumption and 50% NOx emissions reductions were achieved. The Modern DFI Gasoline Engine, continued:  The Modern DFI Gasoline Engine, continued Advances in control systems enables direct-injection stratified charge engine to address the NOx emissions problem in new ways. The Modern DFI Gasoline Engine:  The Modern DFI Gasoline Engine Mitsubishi Started production in Japan in Sept 1996 SAE 960600, SAE 970541, SAE 980150, SAE 2001-01-0545 Toyota Started production in Japan in Dec 1996 SAE 970539, SAE 970540, SAE 980157 SAE 2000-01-0530 and 2000-01-0531, SAE 2001-01-0734, 2001-01-0734 Nissan Started production in Japan in Dec 1997 SAE 980149, SAE 1999-01-0505 Slide46:  Engine Speed Torque Late-Injection, Lean Stratified-Charge Combustion Lean Homogeneous- Charge Combustion Stoichiometric Homogeneous-Charge Combustion 2-Stage Injection Toyota’s Map of Combustion Regimes (SAE 970540) Slide47:  BENEFITS Fuel economy Increased output torque Reduced cold-start HC emissions Improved transient fuel control Reduced HC emissions Increased responsiveness Deccel. Fuel cut-off Close-coupled catalyst protection Idle fuel shut-off Faster low-temperature starting CHALLENGES Cost HC & NOx emissions Combustion control over operating range Injector durability Injector packaging Smoke Low exhaust temperatures First-Order Benefits and Challenges Slide48:  Direct-Injection Gasoline engines offer the potential for significant fuel economy gains. Rapid engine-development progress is being made due to progress in DI fuel systems, control systems and lean-NOx catalysts technology. Rate of introduction into world markets will primarily depend on rate of solving emissions problems and rate of cost reduction. SUMMARY CONCLUSION:  CONCLUSION Direct-Injection Stratified-Charge Gasoline Engines have significantly higher fuel economy than conventional throttled engines; but they also have significantly higher HC and NOx emissions. However, due to recent significant advances in Direct-Fuel-Injection system technology, engine control systems, exhaust aftertreatment systems and understanding of lean and direct-injection combustion processes, revisiting the DISC engine is warranted. Slide50:  1. C. D. Wood, “Unthrottled Open-Chamber Stratified-Charge Engines”, SAE Paper 780341, 1978. 2. A. J. Giovanetti, et al., “Analysis of Hydrocarbon emissions in a Direct-Injection Spark-Ignition Engine”, SAE Paper 830587, 1983. 3. A. S. P. Solomon, “A Photographic Study of Fuel Spray Ignition in a Rapid Compression Machine,” SAE Paper 860065, 1986. 4. Fu-Quan Zhao, Ming-Chia Lai and David L. Harrington,”A Review of Mixture Dynamics and Combustion Control Strategies in Spark-Ignited Direct Injection Gasoline Engines” SAE Paper 970627. 5. Direct-Injection SI Engine Technology, SAE Special Publications: SP-1416, 1999. 6. Direct Fuel Injection for Gasoline Engines, SAE Progress in Technology Series, PT-80, Edited by Arun Solomon, Richard Anderson, Paul Najt and Fuquan Zhao, 2000. Suggested Reading

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