Advanced Hydrogen-Fueled Engines: Potential and Challenges

Christopher WhiteUniversity of New Hampshire

Sandia National Laboratories

ERC Symposium: Fuels for Future Internal Combustion Engines

University of Wisconsin Madison

June 6, 2007

Sandia Sponsor: DOE Office of FreedomCAR and Vehicles Technologies

Program Manager: Gurpreet Singh

Why hydrogen fueled internal combustion engines (H2ICE).

Need for advanced H2ICEs─ relative to conventional port-fuel-injected (PFI) H2ICEs

Example advanced H2ICE strategies

Sandia National Laboratories H2 Engine Program─ objective and approach

─ brief discussion of experiments and results

Summary

Presentation outline

The energy problem

0

100

200

300

400

500

600

700

1990 1995 2000 2005 2010 2015 2020

Qu

ad

rill

ion

s o

f B

TU

s

China

Other

Developing

EE/FSU

Other

Industrialized

United States

Energy Demand Increasing

0.00

10.00

20.00

30.00

40.00

50.00

60.00

1930 1980 2030 2080 2130 2180

Year

Gb

/a

2050Actual 2000

Usage

~25 Gb/a

ConventionalReserves

Conventional + Non-conventionalReserves

Limited Oil Reserves

Where are we going to get this amount

of energy and not harm the environment?CLI

MATE

Hydrogen is an attractive option

It’s clean, promotes highly efficient end-use technologies, and canbe derived from diverse domestic resources.

.

DistributedGeneration

TransportationBiomass

HydroWindSolar

Coal

Nuclear

NaturalGas

Oil

Wit

h C

arb

on

Se

qu

es

tra

tio

n

HIGH EFFICIENCY & RELIABILITY

ZERO/NEAR ZEROEMISSIONS(including CO2)

From Patrovic & Milliken (2003)

Transportation sector has the greatest needs

Electricity Transportation Residential

Coal 48 Oil 3 96 8 Natural Gas 17 3 27 Hydro 9 Electricity 1 62 Renewable 3 Nuclear 19 Solar 2 Hydrogen x Wind 2

% Fuel use by sector

1999 Total 1500 MMT

Gas TurbineCoal Fired STIC EnginesOther BurnersOther Sources546.4

MMT

36%

226.6MMT

15%270.1MMT

18%

411.4MMT27%

66.7MMT

4%

PCPC

11%11%

265.8MMT

16%

474.6MMT

28%

284.1MMT

17%

598.4MMT34%

81.2MMT

5%

PCPC

13%13%

2020 Total 1700 MMT

U.S. CO2 Emission by Combustion Source

Why not hydrogen?

Two main reasons why we do not live in a hydrogen economy:(1) Infrastructure (Production and Distribution)─ How to produce H2 economically and cleanly (without CO2 emissions).

─ Delivery of H2 from production facilities to fueling stations.

(2) Storage─ Difficulty is the low volumetric energy density of gaseous H2.

The requirements of (1) and (2) directly depend on the end-use technolog─ in particular the availability and fuel efficiency (among others).

Regarding the availability, the chicken and egg analogy often (yetwrongly)enters the discussion. This is wrong (especially from a businessmodel) since infrastructure and end-use technologies must developin tandem.End-Use Technologies: PEM Fuel Cell: Projected Cost $300/kW, Efficiency ?? ( 40 ─ 60% Peak)H2ICE: Projected Cost $30/kW, Efficiency 40 ─ 45% Peak

Technology is available today and economically viable in the nearterm.

Number of test/demo vehicles: Ford, BMW among others (seebelow).

• demonstrated efficiencies in excess of today’s gasoline engines.

• near-ZEV (Zero Emission Vehicle) performance

Fewer constraints concerning H2 storage compared to fuel cells.• relative ease of a dual-fuel option (H2/gasoline).

• impurities are a non-issue

Hydrogen-fueled internal combustion engines: An enabling technology to a hydrogen economy

Integral part of DOE's transitional strategy towards a hydrogen economy • www.hydrogen.energy.gov/pdfs/hydrogen_posture_plan.pdf

DOE's near-term goals for the H2ICE (same as for fuel cell vehicle): • peak brake thermal efficiency (BTE) 45%.

• Tier2/bin5 emissions or better (NOx 0.07g/mile).

• power densities greater than present-day gasoline engines.

Research is required to resolve technical barriers to meet these goals. • fundamental research of in-cylinder combustion and transport processes.

• NOx emissions and control.

• advanced H2ICE concepts and related technical issues:

DOE’s interest in H2ICEs

The unique combustion properties of hydrogen can be beneficial atcertain engine operating conditions and pose technical challenges atother engine operating conditions.

H2 properties relevant to ICEs

29.539.48 2†stoich. volume fraction (%)

> 12014091-99research octane number

1.850.380.37-0.43laminar flame velocity (m/s) ‡

2.9

45.8

2.1

0.28

723

2214

0.4-1.6

CNG

2.83

44.79

2

0.24

550

2580

0.7-4

Gasoline

2480adiabatic flame temp. (K)‡

0.1-7.1flammability limits ( )

3.37heat of combustion (MJ/kgair) ‡

119.7lower heating value (MJ/kg)

0.64quenching distance (mm) ‡

858autoignition temp. (K) ‡

minimum ignition energy‡

Property

0.02

Hydrogen

† gasoline vapor, ‡ stoichiometric mixture

wide flammability range(ultra-lean operation)

high flame speeds(good stability)

high compression ratios withimproved thermal efficiency

air displacement effects

propensity to preignite

thin thermal boundary layers

favorable unfavorable

0 0.5 1 1.5 2 2.5 3 3.5 410

-2

10-1

100

101

minimum ignition

hydrogen

heptane

propane

H2 is predisposed topreignition

Preignition: Ignition of the fuel/air mixture before the spark plug fires.

Ignition sources include engine hot spots, oil contaminants, and others.

Produces engine knock-like effects than can lead to engine damage.

Conventional port-fuel-injection(PFI) H2ICEs fueled by compressedH2 gas are most susceptible topreignition.

The preignition problem

In practical applications it is verydifficult to operate a PFI H2ICE at ornear = 1.

Profound effects on peak powerdensityand emissions (NOx) control.

Primarily responsible for the need foradvanced H2ICE options.

Compared to PFI-gasoline,PFI H2ICEs have:

higher thermal efficiencies. • lean unthrottled operation

• operate at higher CR

lower power densities. • theoretical value 85%

• lower value owing to a

preignition limited maximum

fuel-to-air ratio (max 0.7).

Baseline PFI H2ICEs:Brake Thermal Efficiency (BTE)

0 0.2 0.4 0.6 0.8 1 1.20

0.1

0.2

0.3

0.4

BMEP* BMEP / BMEPmax-gasoline

BTE PFI-gasoline

Compression ratio (CR) = 9.1

(CR=14.5), (CR = 12.5) Tang et al. SAE 2002-01-

0242. (CR=9.1) Swain et al. , SAE 810350.

Demonstrates the needfor advanced H2ICEoptions.

0 0.25 0.5 0.75 1 1.25 1.510

0

101

102

103

104

NOx, ppm

CARB, SULEV NO

x < 0.02 g/mile

US Federal Tier II NO

x < 0.07 g/mile Near-ZEV Performance

Three principal strategies:

operate ultra-lean ( < 0.45).

operate with a lean NOx trap. operate at stoichiometry ( = 1)

with 3-way catalyst (TWC).

(preignition problems for a PFI

H2ICE limits this option)

Baseline PFI H2ICEs:Emissions (NOx)

, (closed symbols) engine out

, (open symbols) aftertreatment with 3-way catalyst

NOx is the only non-trivialengine-out emission pollutant─ statement ignores the upstream

emissions in producing hydrogen

Cold-start emissions is a non-issue─ gaseous fuel

Demonstrates the needfor advanced H2ICEoptions.

Advanced H2ICE options

Pressure boosting using supercharging or turbochargingBenefit ─ improved power density by forcing more air into cylinder

Disadvantage ─ higher inlet temperature (exacerbates preignition and NOx)

Liquid Hydrogen fuelingBenefit ─ improved power density, mitigate preignition

Disadvantage ─ energy penalty of liquefaction, cryogenics

Direct InjectionBenefit ─ improved power density, mitigate preignition, charge stratification

Disadvantage ─ short available mixing times (poor mixture preparation)

HybridizationBenefit ─ improved power density, improved efficiency

Disadvantage ─ system complexity

Multi-mode strategies

Benefit ─ improved power density, improved efficiency, mitigate preignition

Disadvantage ─ system complexity

Continuous ultra-lean ( < 0.45) operationwith improved power densities

H2ICE-electric

hybrid

Ford H2RV

SC 2.3L I4-engine

30 HP Electric Motor

Fuel economy: 45 miles/kg

Emissions: SULEV or better

Ford H2ICE-450 shuttle

SC 6.8L V10-engine

Fuel economy: 7 miles/kg

Emissions: SULEVor better

pressure boosting

(turbo or SC)

SC 2.3L I4-engine

Fuel economy: 37 miles/kg

Emissions: SULEV or better

Ford H2ICE Focus

Advanced H2ICE strategies (1)

Accessible stochiometric ( = 1) operationwith aftertreatment

liquid hydrogen

fueling

cold mixture prevents

preignition and allows = 1 operation

exhaust gas

dilution (EGR)

lean-burn conditions

are diluted with EGRsuch that = 1

(no excess oxygen)

direct injection

DI-H2ICE

injection timing is

optimized (delayed) to

prevent preignition

and allow for = 1 operation

= 0.6 (excess air)

= 1.0 (EGR dilution)

Advanced H2ICE strategies (2)

Multi-mode strategies

liquid hydrogenfueling

BMW 745h

ultra-lean ( < 0.45) operation

low engine load

stochiometric ( = 1) operation

with aftertreatment

medium engine load

exhaust gasdilution (EGR)

high engine load

4.4L V8-engineFuel economy: 25 miles/kg

Emissions: Significantly below SULEV

Advanced H2ICE strategies (3)

Multi-mode strategies

ultra-lean ( < 0.45) operation

low engine load

Emissions: Significantly below SULEV

medium engine load

pressure boosting

supercharger

Ford H2ICE Focus

high engine load

Lean ( 0.7) operationLean NOx Trap (LNT)

Advanced H2ICE strategies (4)

Numerical ProgramExperimental Program

Single-cylinder optical test engine Apply advanced laser-based

optical diagnostics.

High-fidelity numerical simulations using the Large Eddy Simulation (LES) technique.

Massively parallel computation facilities

One-To-One CorrespondenceBetween Simulations and

Engine Experiments

Sandia H2ICE program

Approach

Experimental approach: systematic development of experimentaltechniques to assess in-cylinder H2-air mixing.(1) OH* chemiluminescence imaging combustion and mixture distribution.

(2) Planar Laser Induced Fluorescence (PLIF) H2 concentration

(3) Particle Image Velocimetry (PIV) in-cylinder velocity field.

provide experimental data to validate numerical schemes, grid resolution,

and models implemented in the Large Eddy Simulations.

focus on speed/load conditions that are of value to Ford, complement

similar efforts at ANL, and accessible in an optical engine.

A combined study using laser-based experimental techniques in anoptically-accessible engine and high fidelity numerical simulations isemployed to obtain a physical understanding of the in-cylinder transportprocesses (concentration and temperature) in a DI H2ICE.

Mixture stratification in a DI H2ICE (Tech. Barriers)

0204060801001200

2000

4000

6000

8000

10000

SOI (oBTDC)

NO

x (ppm)

Conjecture:Mixture inhomogeneities

Effect of start-of-injectionon NOx emissions

low NOx high NOx low NOx

overall = 0.3

well-mixed

stratified

well-

mixed

= 0.8 = 0.3Mixture

formation

NOxNOx

Similar effects of SOI on BTE. It is therefore critical to develop a

knowledge base of in-cylinder transport processes in a DI H2ICE

Optical test engineGM single-cylinder head

4 valves, central spark plug

560 cm3 displacement

CR: 9.1-10.3 (flat piston)

Optical access

interchangeable quartz liner

interchangeable quartz piston

Hydrogen fueling

side direct injection

six-hole, 90o cone angle

(Westport Innov.)

injector

spark plug

intake

exhaust

quartzquartzwindowswindows

Sandia optical H2 engine facility

OH* chemiluminescence measurements

natural luminosity of excited state OH (OH*) line of sight measurement qualitative (at best semi-quantitative)

imaged field-of-view

Flame front propagation speed:“Pre-mixed” H2-air mixture

time.is and radius flame theis where, trdt

dCAD

dCAD

dru f

f

f =

Use H2O mass fraction

to track flame front propagation

LES Validation (first attempts)Flame front propagation speed

Acetone PLIF measurements in the optical engine

inject a mixture of 99.5% H2 and 0.5% acetone (seed) by volume. 266 nm laser sheet used for acetone excitation

imaged field-of-view

PLIF images compared to OH* chemiluminescence images:Evaluating in-cylinder mixture distribution

Engine conditions are fixed: — Pinj = 5MPa; 0.5

PLIF images acquired -32 CAD BTDC OH* images acquired at 10% AHR

PLIF images OH* images

Interpretation of these imagesrevealssimilar results with respect tomixture distribution:(1) SOI at IVC produces a “near-

homogeneous” mixture (top images). radial propagating flame front in the OH*

image is indicative of being well-mixed.

(2) Mixture inhomogeneities increase

with increasing retard of SOI from IVC.

(3) With late injection, H2 is

concentrated in small volumes spatially

located near the injector (bottom

images).

retardSOI

IVC

Summary

Hydrogen is an attractive fuel for future internal combustionengines.

H2ICEs will serve as an enabling end-use technology for building a hydrogen economy. • demonstrated efficiencies in excess of today’s gasoline engines.

• near-ZEV (Zero Emission Vehicle) performance

DI H2ICE is one of the most attractive advanced H2ICE options. • high power density

• mitigate preignition problems

• optimal charge stratification has the potential for:

- improved efficiency

- reduced emissions

Further research required to resolve technical barriers. • robust high pressure, high flow rate H2 injectors

• fundamental understanding of in-cylinder transport processes.