Department of Mechanical Engineering, Iowa State University

1

Performance of a Compression-Ignition

Engine Using Direct-Injection of Liquid

Ammonia/DME Mixture

Song-Charng Kong

Matthias Veltman, Christopher Gross

Department of Mechanical Engineering

Iowa State University

Acknowledgements:

Iowa Energy Center;

Norm Olson, Kevin Nordmeyer

Department of Mechanical Engineering, Iowa State University 2

Background

• Motivation

• Ammonia (NH3) combustion does not generate CO2

• Hydrogen carrier, renewable, etc.

• Challenges

• Ammonia is very difficult to ignite

• Octane number ~ 130

• Autoignition T ~ 651 ºC (gasoline: 440 ºC; diesel: 225 ºC)

• Ammonia flame temperature is lower than diesel flame T

• Ammonia emissions can be harmful

• Potential high NOx emissions due to fuel-bound nitrogen

• Gas phase at atmospheric pressure; Erosive to some materials

• Low energy content (~40% of that of diesel fuel per unit mass)

Department of Mechanical Engineering, Iowa State University 3

Thermodynamics/Chemistry

• Stoichiometric chemical reaction

3 2 2 2 20.75 ( 3.76 ) 1.5 3.32NH O N H O N

Fuel Molecule Boiling

Point (°C) (Air/Fuel)s

Latent

Heat

(kJ/kg)

Energy

Content

(MJ/kg-fuel)

Energy Content

(MJ/kg-

stoichiometric

mixture)

Methanol CH3OH 64.7 6.435 1203 20 2.6900

Ethanol C2H5OH 78.4 8.953 850 26.9 2.7027

Gasoline C7H17 --- 15.291 310 44 2.5781

Diesel C14.4H24.9 --- 14.3217 230 42.38 2.7660

Ammonia NH3 –33.5 6.0456 1371 18.6103 2.6414

Department of Mechanical Engineering, Iowa State University 4

Approach #1

• Introduce ammonia to the intake manifold

• Create premixed ammonia/air mixture in the cylinder

• Inject diesel fuel to initiate combustion

• Without modifying the existing injection system

Diesel ignition

Induce NH3

combustion

Burn out

premixed NH3

Department of Mechanical Engineering, Iowa State University 5

Engine Setup

• John Deere (4 cylinder, 4.5 liter)

• Operated at various load and speed conditions

• Vapor ammonia introduced into the intake duct – after turbo,

before manifold

Induction

point

Liquid NH3 tank

Fuel line

Fuel line

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Test Results – Constant NH3 Flow Rate

• Engine torque increases suddenly once ammonia is

inducted

0

100

200

300

400

500

-80

-60

-40

-20

0

20

40

0 20 40 60 80 100 120

1800rpm Engine Torque

Engin

e T

orq

ue

(ft-lb)

Energ

y b

y N

H3 (%

)

Engine Load (%)

Diesel baseline

Diesel+ NH3

Energy replacement

by NH3

0

100

200

300

400

500

-50

0

50

0 20 40 60 80 100 120

1400rpm Engine Torque

Engin

e T

orq

ue

(ft-lb)

Energ

y b

y N

H3 (%

)

Engine Load (%)

Diesel baseline

Diesel+ NH3

Energy replacement

by NH3

Department of Mechanical Engineering, Iowa State University

• Fixed at specific diesel fueling, adjusted NH3 flow

rate to maintain constant torque

• Can achieve 5% diesel / 95% NH3 energy ratio

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

Power Contribution from Diesel Fuel (%)

Po

we

r (k

W)

Diesel Only

NH3 + Diesel

Contribution

from NH3

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

Power Contribution from Diesel Fuel (%)

Po

we

r (k

W)

Diesel Only

NH3 + Diesel

Contribution

from NH3

7

Test Results – Constant Torque

from

NH3

diesel

Department of Mechanical Engineering, Iowa State University

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100

Power Contribution from Diesel Fuel (%)

NH

3 (

pp

mV

)

8

NH3 Exhaust Concentrations

• Concentrations vary depending on NH3 fueling rate

• Further study is required to reduce NH3 emissions.

High NH3

fueling

Low NH3

fueling 20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

Constant Engine Torque

Ma

ss C

on

ve

rsio

n E

ffic

ien

cy (

%)

Diesel Load (%)

Ammonia combustion

efficiency

Department of Mechanical Engineering, Iowa State University

Approach #2

• Use direct liquid fuel injection

• Confine combustion mixture near the center

• To reduce exhaust ammonia emissions

• Ignition source – dimethyl ether (CH3-O-CH3)

• Mixture of DME and NH3

• Fuel mixing and storage at high pressure

• New fuel injection system – without fuel return

• Injection pump, injector, electronic control

9

Fuel injector

Department of Mechanical Engineering, Iowa State University

Engine Setup

• Yanmar diesel engine (L70V, 320 c.c.)

• Rated power at 6.26 hp at 3480 rpm

• Develop new fuel injection and engine control systems

• Bosch GDI type injector (up to 200 bar injection pressure)

Department of Mechanical Engineering, Iowa State University

Setup

• Mixing and storage of ammonia/DME at high pressure

• Exhaust emissions measurements

• Horiba MEXA-7100DEGR (CO2, CO, O2, HC)

• Horiba 1170NX (NOx, NH3)

• AVL Smoke Meter (PM)

Fuel mixing system

Emissions analyzers

Department of Mechanical Engineering, Iowa State University

Operating Conditions

12

Operating map using original diesel injection system

Department of Mechanical Engineering, Iowa State University

Test Results

• Baseline operation using 100% DME

• Explore operating range before using NH3/DME mixture

• For each operating point, various start-of-injection timings

were tested

• Provide flexibility for future optimization

13

SOI= –25 ~ 5 BTDC SOI= –30 ~ 0 ATDC

SOI= –35 ~ 20

BTDC

SOI= –30 ~ 20 BTDC

SOI= –30 ~ 20 BTDC

Department of Mechanical Engineering, Iowa State University

100% DME

• Mode 7 (2548 rpm) emissions

14

0

0.002

0.004

0.006

0.008

0.01

0

100

200

300

400

500

-30 -25 -20 -15 -10 -5 0

100% DME

Soo

t (F

SN

)

NO

x (p

pm

)

SOI (ATDC)

Soot - Smoke number

NOx

0

500

1000

1500

2000

-30 -25 -20 -15 -10 -5 0

100% DME

CO

& H

C (

pp

m)

SOI (ATDC)

CO

HC

Department of Mechanical Engineering, Iowa State University

Effects of Ammonia Combustion (Mode 7)

• 100%DME vs. 20%NH3/80%DME

• Soot remains at low level

• NOx increases due to fuel-bound nitrogen

15

0

0.002

0.004

0.006

0.008

0.01

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

Soo

t (F

SN

)

SOI (ATDC)

100%DME

20%NH3/80%DME

0

100

200

300

400

500

600

700

800

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

NO

x (

pp

m)

SOI (ATDC)

100%DME

20%NH3/80%DME

Department of Mechanical Engineering, Iowa State University

Effects of Ammonia Combustion (Mode 7)

• 100%DME vs. 20%NH3/80%DME

• Lower combustion temperature of ammonia causes more CO

and HC emissions

• Implication to fuel efficiency

16

0

500

1000

1500

2000

2500

3000

3500

4000

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

CO

(p

pm

)

SOI (ATDC)

100%DME

20%NH3/80%DME

0

100

200

300

400

500

600

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

HC

(pp

m)

SOI (ATDC)

100%DME

20%NH3/80%DME

Department of Mechanical Engineering, Iowa State University

Effects of Ammonia Combustion (Mode 21)

• Comparable combustion and fuel efficiency at this

lower speed

17

0

0.005

0.01

0.015

0.02

-35 -30 -25 -20 -15 -10 -5 0 5

Mode 21 (2200 rpm)

So

ot

(FS

N)

SOI (ATDC)

100%DME

20%NH3/80%DME

0

100

200

300

400

500

600

-35 -30 -25 -20 -15 -10 -5 0 5

Model 21 (2200 rpm)

NO

x (

ppm

)

SOI (ATDC)

100%DME

20%NH3/80%DME0

500

1000

1500

2000

2500

0

500

1000

1500

2000

2500

-35 -30 -25 -20 -15 -10 -5 0 5

Model 21 (2200 rpm)

100%DME

20%NH3

DME-HC

20%NH3

CO

& H

C (

pp

m)

SOI (ATDC)

CO

HC

Department of Mechanical Engineering, Iowa State University

Effects of Ammonia Combustion

• Exhaust ammonia emissions much lower than Approach#1

• Direct injection strategy benefits exhaust ammonia

emissions

18

0

50

100

150

200

250

300

350

400

-40 -35 -30 -25 -20 -15 -10 -5 0

NH3 Emissions (20%NH3/80%DME)

NH

3 (

pp

m)

SOI (ATDC)

Mode 7 (2548 rpm, low)

Mode 20

(2200 rpm, medium)

Mode 21 (2200 rpm, low)

Department of Mechanical Engineering, Iowa State University

Alternate Injection Strategy

• To extend the operating range

• Proposed strategies

• Double fuel injections

• Offer flexibilities in fuel delivery

• Used in industry for emissions and noise

reduction

• New fuel injector

• Original: single hole

• Alternate: eight holes – help with air

utilization

19

x % (100–x) %

pilot main

Department of Mechanical Engineering, Iowa State University

Double Injection, 100% DME

• Current system modified for using double injections

• Engine operations possible using double injections

• Comparable fuel efficiency and emissions

• Results based on Mode 7 (2548 rpm)

• Pilot SOI= –45 ~ –35 ATDC

• Pilot quantity=30% of total fuel

• Main SOI= –10 ATDC

• Exploring other conditions

• Varying the three injection variables

• Other operating points

20

0

0.002

0.004

0.006

0.008

0.01

300

350

400

450

500

550

600

-50 -45 -40 -35 -30

Double Injections (Mode 7)

So

ot

(FS

N)

NO

x (p

pm

)

Pilot SOI (ATDC)

Soot - Smoke number

NOx

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Multi-Hole Injector

• Change from single hole to 8 holes

• Higher exhaust NOx – may imply higher combustion

temperature to sustain higher load operation

• Exploring combination of using 8-hole injector in

combination with double injections

21

0

0.005

0.01

0.015

0.02

0.025

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

Soo

t (F

SN

)

SOI (ATDC)

Single hole

8 holes

0

100

200

300

400

500

600

-30 -25 -20 -15 -10 -5 0

Mode 7 (2548 rpm)

NO

x (

pp

m)

SOI (ATDC)

Single hole

8 holes

Department of Mechanical Engineering, Iowa State University 22

Summary

• Demonstrated ammonia combustion in diesel engines

• Port induction of ammonia coupled with direct-injection

diesel fuel

• Exhaust ammonia level at “thousands of ppm” under the

conditions studied

• Direct injection of ammonia/DME

• Exhaust ammonia level at “hundreds of ppm” under the

conditions studied

• Exploring optimal injection strategies for ammonia combustion

• Perspectives – effects of engine size

• Challenges for small engine: more heat loss, higher engine speed

required, lower fuel injection pressure

• Large engine will favor ammonia combustion