Fuel Requirements for HCCI Engine Operation. Tom Ryan Andrew Matheaus Southwest Research Institute

Transcription

1 Fuel Requirements for HCCI Engine Operation Tom Ryan Andrew Matheaus Southwest Research Institute 1

2 HCCI Fuel & Air Charge Undergoes Compression Spontaneous Reaction Throughout Cylinder Low Temperature and Fast Reaction Gives Low NO x 2

3 Fundamentals of HCCI Reaction 1 Ideally, a Homogeneous Fuel-Air Mixture is One in Which the Composition and the Thermodynamic Conditions are Uniform Throughout the Reaction Phase Reaction Starts When the Thermodynamic Conditions are Sufficient to Initiate Chain Branching Reactions Reaction Rates and Reaction Duration are Kinetically Controlled 3

4 Fundamentals of HCCI Reaction 2 Practical Fuel-Air Mixtures Have Both Compositional and Thermodynamic In-Homogeneities Reaction Begins in the Fuel Richest and the Highest Temperature Locations Reaction Rates and Reaction Duration are Affected by Mixing and Heat Transfer 4

5 Port Injection Configuration Air-Assist Pressure- Swirl Injector Timed to Valve Opening Liquid Drops Acceptable Evaporation During Compression 5

6 HCCI Development Problems SOR Control No SOR Property Defined Mixture Preparation Total Evaporation Before the Start of Reaction 6

7 Typical HCCI Engine Heat Release Heat Release Rate (BTU/ ) Main Heat Release Inital Heat Release Ignition Delay Crank Angle ( ) 7

8 Start of Reaction Effects of Compression Temperature History Crank Angle ( ) Various Intake Temperatures and EGR In All Cases SOR is Very Near 650 K 8

9 Mixture Preparation Effects of Intake Temperature Bosch BSN Smoke Number Diesel, CR=14 20% Blend CR=14 40% Blend CR=14 60% Blend CR=14 80% Blend CR= Intake Air Temperature Temp. (C) (C) Slight BSN Advantage With Blends Critical Temp. For These Conditions 150C Naphtha & Gasoline Had Zero BSN for All Conditions 9

10 SOR and Mixture Preparation Effects of Intake Temperature Intake Manifold Temp. (C) Start Of Reaction (CAD) Diesel, 14 CR 20%, 14 CR 40%, 14 CR 60%, 14 CR 80%, 14 CR Gasoline, 16 CR Naphtha, 14 CR Naphtha, 16 CR All Fuels Advanced SOR Compared to Diesel Naphtha Operates at Lower Intake Temp. 10

11 HCCI Rules Fuel Related All Fuel Must Be Evaporated Prior to the Start of Reaction Liquid Fuel Drops Burn As Diffusion Flames With High NOx and PM Fuels Must Have Start of Reaction Temperatures and Ignition Delay Times (Ignition Characteristics) Such That Reaction Begins at TDC 11

12 Fuel-Blending with Two Fueling Systems Upstream mixing of natural gas Air-assisted port injection of F-T naphtha This engine s fuel system accommodates one gaseous fuel and one liquid fuel 12

13 Choice of Fuels Used Natural Gas used because: This engine was already equipped with fuel system engine can still be operated at full load on spark-ignited natural gas fueling Natural gas has low reactivity (high-octane number) F-T naphtha used because: It is sufficiently volatile for use with port injection Its auto-ignition characteristics work with this compression ratio Other fuels can be used with this engine concept with slight modifications 13

14 Combustion Phasing Control Through Fuel-Blending High reactivity (low-octane) fuel Intake Air Low reactivity (high-octane) fuel Exhaust More reactive mixture advances combustion Less reactive mixture retards combustion Premise for this approach: By altering the propensity of the air-fuel mixture to autoignite, it is possible to control the combustion phasing 14

15 Single-Fuel HCCI Heat Release Rate (Arbitrary Units) Multi-Cylinder Engine on F-T Naphtha Increasing F-T Naphtha Amount Crank Angle Degrees 1000 RPM (approx.) 97 kpa MAP Inceasing F-T Naphtha No Natural Gas Varying the amount of F-T naphtha changes the combustion phasing (when no gas is used) This is the typical problem experienced with HCCI combustion of a single fuel Typical HCCI combustion phasing advance with increasing load and vice-versa 15

16 Fuel-Blending Approach Heat Release Rate (Arbitrary Units) Mutli-Cylinder Engine on F-TNaphtha and Natural Gas 1000 RPM (approx.) 97 kpa MAP Constant Amount of F-T Naphtha Increasing Natural Gas 0 No Natural Gas Crank Angle Degrees Increasing Natural Gas Amount Dual-fuel HCCI combustion phasing is not affected by low-reactivity fuel (natural gas) amount 16

17 Start of Reaction Effects of Compression Temperature History Crank Angle ( ) Various Intake Temperatures and EGR In All Cases SOR is Very Near 650 K 17

18 IQT Description The IQT is a Constant Volume Combustion Bomb Apparatus The System Includes: Heated Pressure Vessel Single Shot Fuel Injection System System Controller Data Acquisition System 18

19 IQT Pressure Vessel and Injection System 19

20 IQT Pressure Vessel 20

21 IQT Fuel Injection System 21

22 IQT Controller and Data Acquisition System 22

23 IQT Operation The Pressure Vessel is Charged with Air at High Pressure and Heated to the Test Temperature Fuel is Injected Needle Lift and Vessel Pressure are Recorded and used to Determine the Ignition Delay and Other Parameters 23

24 IQT Raw Data 24

25 IQT CN Calibration Calibration Shift is Minor Calibration Checked Daily 25

26 IQT Application HCCI Fuel Rating Octane Number and Cetane Number were Developed for SI and CI Engine Applications Developments were Evolutionary HCCI Results Indicate that Neither are Adequate for Reflecting the SOR in an HCCI Engine Data Indicates that some Measure of Autoignition Temperature (AIT) is Needed Elevated Pressure AIT Defined in IQT 26

27 EPAIT Measurement in IQT IQT Used to Measure the Elevate Pressure AIT (EPAIT) Tests Done at Different Temperatures A Fixed Ignition Delay Time is Selected and Used to Define the Ignition Temperature Delay Time, ms EHN in FT Diesel Fuel ppm EHN ppm EHN Temp, o C 27

28 Fuels Tested IGNITION DELAY (ms) IGNITION DELAY (ms) HEXADECANE 80% HEXADECANE / 20% HEPTAMETHYLNONANE 60% HEXADECANE / 40% HEPTAMETHYLNONANE 40% HEXADECANE / 60% HEPTAMETHYLNONANE 20% HEXADECANE / 80% HEPTAMETHYLNONANE Neat Heptamethylnonane not shown TEST TEMPERATURE ( o C) 6 0 ppm EHN 500 ppm EHN ppm EHN 2000 ppm EHN ppm EHN 4000 ppm EHN IGNITION DELAY (ms) TEST TEMPERATURE ( o C) DIESEL 80% DIESEL / 20% GASOLINE 60% DIESEL / 40% GASOLINE 40% DIESEL / 660% GASOLINE 20% DIESEL / 80% GASOLINE GASOLINE IGNITION DELAY (ms) Fuels Tested: ON Reference Fuel Blends CN Reference Fuel Blends FT Naphtha + EHN Gasoline-DF2 Blends 80% ISOOCTANE / 20% nheptane 60% ISOOCTANE / 40% nheptane 40% ISOOCTANE / 60% nheptane 20% ISOOCTANE / 80% nheptane nheptane ISOOCTANE not shown on this graph TEST TEMPERATURE ( o C) TEST TEMPERATURE ( o C) 28

29 Data Conversion Temperature, o C T = exp( td) Delay Time, ms FT Additized with EHN Need Temperature at Ignition for Different Ignition Delay Times Simple Inversion and Regression Inverted Data Used to Interpolate and Extrapolate to Define a Common Delay time 29

30 Octane Number vs Cetane Number Octane Number ON = *CN *CN *CN Cetane Number 30

31 EPAIT vs CN Elevated Pressure Autoignition T Elevated Pressure Autoignition Temperature vs Cetane Number Hexadecane-Heptamethylnonane Isooctane-Heptane DF2-Gasoline Fischer Tropsch-EHN Cetane Number CN Has Some Relationship to EPAIT CN Does Not Universally Relate to EPAIT ON Relationship is Worse Than the CN Relationship 31

32 EPAIT vs ON The ON Relationship is not as Good as the CN Relationship Negative ON is Possibly Meaningless More Deviation with the Additized Fuel Shape Inflection Makes Definition of EPAIT Difficult Elevated Pressure Autoignition T Hexadecane-Heptamethylnonane Isooctane-Heptane DF2-Gasoline Fischer Tropsch-EHN Octane Number 32

33 Correlation IQT-EPAIT Data and Engine Data SOR in the Engine is Based on the Pre- Reaction SOR Predicted using an Arrhenius Type Rate Expression Verified by Engine HRR Measurements Correlation is Fair SOR ( o C) ms ( o C) 33

34 Future of HCCI Method Need to Test More Fuels in both the IQT and the HCCI VCR Engine Follow the IQT Test Method Described Engine Tests in SwRI VCR Test Engine Test Fuels: More GTL Products Petroleum Naphtha Fractions Additized ON Reference Fuel Blends Additized Gasolines Alternative Fuels Relate to SOR In the Engine 34