DUAL-FUEL HCCI ENGINE EXPERIMENTS WITH PRIMARY REFERENCE FUELS Ali - - PowerPoint PPT Presentation

DUAL-FUEL HCCI ENGINE EXPERIMENTS WITH PRIMARY REFERENCE FUELS

Ali Aldawood 1,2, Sebastian Mosbach 2, Markus Kraft 2, Amer Amer 1

1 Saudi Aramco 2 University of Cambridge

Presented by: Gautam Kalghatgi, Saudi Aramco

Outline

• Introduction
• Dual-fuel effects
• Intake temperature effects
• Summary

Introduction

• Examine effects of fuel reactivity on HCCI operating limits,

and overall feasibility of the dual-approach for extending HCCI operating range

• Intake air temperature effects on engine operation stability

and lower load limit, and feasibility of combining intake air heating with dual-fuel approach

Experimental Detail

• Single-cylinder engine – 0.5 L PFI –
• PRF (iso-octane and n-heptane) fuels of 40, 60, 80 ON
• Intake pressure and back pressure fixed at 1.5 bar abs.
• Two intake temperatures - 75˚C and 90˚C
• Three different speeds, 1200, 1500 and 1800 RPM
• Different equivalence ratios
• Pressure data for 300 consecutive cycles
• Emissions – averaged over 60 s at 0.1s interval

Pressure Trace and Heat Release

• 20
• 10

10 20 30 20 30 40 50 60 70 80 90 Cylinder Pressure (bar)

Φ =0.323

0.290 0.258 0.230 0.195

1500 rpm PRF40

• 20
• 10

10 20 30 20 40 60 80 100 120 HRR (J/deg)

Φ =0.323

0.290 0.258 0.230 0.195

CAD (deg)

• 20
• 10

10 20 30 20 30 40 50 60 70 80 90

Φ =0.358

0.346 0.336 0.324

1500 rpm PRF80

• 20
• 10

10 20 30 20 40 60 80 100 120

Φ =0.358

0.346 0.336 0.324

CAD (deg)

• Heat release curves of

PRF40 exhibit two-stage ignition characteristics

• First-stage heat release

becomes weaker as the iso-octane ratio increases

• Load range becomes

narrower and sensitivity

• f pressure history to

equivalence ratio becomes stronger as iso-

• ctane ratio increases

Combustion Phasing

0.1 0.15 0.2 0.25 0.3 0.35 0.4

• 10
• 5

5 10 15 CA50 (ATDC) 1200 rpm 0.1 0.15 0.2 0.25 0.3 0.35 0.4

• 10
• 5

5 10 15 CA50 (ATDC) 1500 rpm 0.1 0.15 0.2 0.25 0.3 0.35 0.4

• 10
• 5

5 10 15 CA50 (ATDC)

Φ

1800 rpm PRF40 PRF60 PRF80 Misfire limit Misfire limit Misfire limit Knock limit Knock limit Knock limit

• Misfire and knock limits are set

following the definitions of HLL (7 MPa/ms) and LLL (5.0% IMEP COV)

• Combustion phasing advances

(almost linearly) with increasing load until reaching the knock limit – Not constant

• The operating window becomes

narrower with increasing speed

Effects on Load Range and Efficiency

• Decreasing fuel reactivity

expands upper load limit and the plateau where ISFC is low and indicated efficiency is high

• This effect becomes more

noticeable as engine speed increases

• Maximum IMEPg of 7.2

bar, maximum indicated efficiency of 44%, and minimum ISFCg of 185.5 g/kW .h are obtained with PRF80 at 1800 RPM

0.1 0.2 0.3 0.4 2 4 6 8 1200rpm Gross IMEP (bar)

PRF40 PRF60 PRF80

0.1 0.2 0.3 0.4 100 200 300 400 500 Gross ISFC (g/kW.h) 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.5 Indicated Efficiency,

η Φ

0.1 0.2 0.3 0.4 2 4 6 8 1500rpm 0.1 0.2 0.3 0.4 100 200 300 400 500 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.5

Φ

0.1 0.2 0.3 0.4 2 4 6 8 1800rpm 0.1 0.2 0.3 0.4 100 200 300 400 500 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.5

Φ

High and Low Load Limits

• Increasing fuel reactivity

increases engine stability at low load but makes the engine more susceptible to knock at higher loads

• Boundaries of efficiency plateau

generally correspond to MPRR

• f aprox. 7 MPa/ms on high load

side and 3.5% IMEP COV in low load side

• Variations in MPRR increase

sharply with increasing speed

0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.5 IMEP CoV 1200rpm 0.1 0.2 0.3 0.4 2 4 6 8

• Max. PRR (MPa/ms)

1200rpm

PRF40 PRF60 PRF80

0.1 0.2 0.3 0.4 0.1 0.2 0.3 IMEP CoV 1500rpm 0.1 0.2 0.3 0.4 2 4 6 8

• Max. PRR (MPa/ms)

1500rpm 0.1 0.2 0.3 0.4 0.2 0.4 0.6 0.8 IMEP CoV

Φ

1800rpm 0.1 0.2 0.3 0.4 2 4 6 8

• Max. PRR (MPa/ms)

Φ

1800rpm

Operating Envelopes for Different Fuels

• Clear potential for variable reactivity

approach

• Operating envelopes shrink with

decreasing fuel reactivity and increasing engine speed

• More reactive fuels allow engine to
• perate with leaner mixtures
• Fuel effects are not linear with octane

number

Fuel Effects on Operating Limits

• LLL and HLL are less sensitive to

changes in octane rating between 40 and 60 than between 60 and 80

• This means that decreasing fuel

reactivity below certain limit does not help in controlling load or extending LLL

• This nonlinear effect necessitates use of
• ther combustion control means to

complement dual fuel approach during low load operation

Intake Temperature Effects

2 4 6 8 0.05 0.1 0.15 0.2 0.25 IMEP CoV 1200 rpm

PRF60-IAT=75oC PRF80-IAT=75oC PRF60-IAT=90oC PRF80-IAT=90oC

2 4 6 8 2 4 6 8

• Max. PRR (MPa/ms)

1200 rpm 2 4 6 8 0.05 0.1 0.15 0.2 0.25 IMEP CoV 1500 rpm 2 4 6 8 2 4 6 8

• Max. PRR (MPa/ms)

1500 rpm 2 4 6 8 0.05 0.1 0.15 0.2 0.25 IMEP CoV Gross IMEP (bar) 1800 rpm 2 4 6 8 2 4 6 8

• Max. PRR (MPa/ms)

Gross IMEP (bar) 1800 rpm

• Increasing intake

temperature improved the engine operating stability at low and intermediate load but increased pressure rise rate at high load.

• Operating envelope shifts at

each speed to lower load side and operation becomes more stable in general

Intake Temperature Effects

• Increasing intake

temperature caused a slight decrease in efficiency at higher loads

• Increasing intake

temperature resulted in consistent reduction in CO emissions

• HC emissions

decreased at low load

1 2 3 4 5 6 7 8 0.1 0.2 0.3 0.4 0.5 1500rpm

Φ

PRF60-IAT=75oC PRF80-IAT=75oC PRF60-IAT=90oC PRF80-IAT=90oC

1 2 3 4 5 6 7 8 100 200 300 400 500 Gross ISFC (g/kW.h) 1 2 3 4 5 6 7 8 0.1 0.2 0.3 0.4 0.5 Indicated Efficiency,

η

Gross IMEP (bar) 1 2 3 4 5 6 7 8 0.5 1 1.5 2 CO(%) 1 2 3 4 5 6 7 8 0.5 1 1.5 2 x 10

4

1500 rpm HC (ppm) 1 2 3 4 5 6 7 8 2 4 6 8 Gross IMEP (bar) NOx (ppm)

PRF60 - IAT=75oC PRF80 - IAT=75oC PRF60 - IAT=90oC PRF80 - IAT=90oC

1 2 3 4 5 6 7 8

• 5

5 10 15 20 CA50 (ATDC)

1200 rpm PRF60-IAT=75oC PRF80-IAT=75oC PRF60-IAT=90oC PRF80-IAT=90oC

1 2 3 4 5 6 7 8

• 5

5 10 15 20 CA50 (ATDC)

1500 rpm

1 2 3 4 5 6 7 8

• 5

5 10 15 20 CA50 (ATDC) Gross IMEP (bar)

1800 rpm

Combustion Phasing

• Increasing intake temperature

caused a slight advance in combustion phasing, especially with PRF60

• This may explain the slight

decrease in efficiency at the higher load

Intake Temperature Effects

• Increasing intake

temperature extended LLL but slightly decreased HLL. Operating envelope, therefore, was expanded more towards the low load region

• Increasing intake

temperature from 75oC to 90oC resulted in an

• perating range

equivalent to that

• btained by decreasing

the PRF octane rating from 60 to 40.

Summary

• Decreasing fuel reactivity results in narrower operating window but

expands high load limit and shifts operation towards higher equivalence

• ratio. These effects became more prominent as speed increased
• Increasing fuel reactivity becomes increasingly less effective in controlling

HCCI combustion as engine load decreases. This nonlinear effect renders reactivity-base control not effective for extending low load limit

• Increasing intake temperature extended low load limit and enabled a

more stable operation in general

• Increasing intake temperature resulted in some positive, but generally not

significant, effects on engine performance and exhaust emissions. Most noticeable effect was the consistent reduction of CO emissions within the low to intermediate load region

Back-up slides

Operating Window

• Boundaries of efficiency plateau

were generally found to correspond to an MPRR of about 7 MPa/ms on high load side and 3.5% IMEP COV in low load side

• Clear correlation between

indicted efficiency and CO and HC emissions

• HLL is set at 7 MPa/ms and LLL

is set at 5% IMEP COV , accepting some penalty in thermal efficiency and CO emissions

0.1 0.15 0.2 0.25 0.3 0.35 2 4 6 8

• Max. PRR (MPa/ms)

0.1 0.15 0.2 0.25 0.3 0.35 0.1 0.2 0.3 IMEP CoV 0.1 0.15 0.2 0.25 0.3 0.35 0.2 0.4 Indicated Efficiency,

η

0.1 0.15 0.2 0.25 0.3 0.35 1 2 CO (%) 0.1 0.15 0.2 0.25 0.3 0.35 1 2 x 10

4

HC (ppm)

Φ

Low load limit High load limit IAT = 75oC 1500 rpm PRF60

0.05 0.35 7.0

Operating range

Engine Test Cell

Displacement 499 cm3 Stroke 90 mm Bore 84 mm Connecting rod 159 mm Compression ratio 12:1 Fuel delivery system PFI

Effects on Emissions - I

0.1 0.2 0.3 0.4 0.5 1 1.5 2 CO (%) 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

HC (ppm) (1200 rpm) 0.1 0.2 0.3 0.4 2 4 6 8 NOx (ppm)

Φ

0.1 0.2 0.3 0.4 0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

(1500 rpm)

PRF40 PRF60 PRF80

0.1 0.2 0.3 0.4 2 4 6 8

Φ

0.1 0.2 0.3 0.4 0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

(1800 rpm) 0.1 0.2 0.3 0.4 2 4 6 8

Φ

• HC emissions plateau around

1500 ppm, but increases sharply as the engine approaches misfire region

• CO emissions show very

strong sensitivity to operating conditions, reach a climax quickly after the misfire starts to occur, and then decreases sharply

• NOx emissions ranged from

less than 1 ppm to 2 ppm in normal operation, but slightly increased close to motoring limit – Reason not clear

Effects on Emissions - II

0.1 0.2 0.3 0.4 0.5 1 1.5 2 CO (%) 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

HC (ppm) (1200 rpm) 0.1 0.2 0.3 0.4 2 4 6 8 NOx (ppm)

Φ

0.1 0.2 0.3 0.4 0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

(1500 rpm)

PRF40 PRF60 PRF80

0.1 0.2 0.3 0.4 2 4 6 8

Φ

0.1 0.2 0.3 0.4 0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 1 1.5 2 x 10

4

(1800 rpm) 0.1 0.2 0.3 0.4 2 4 6 8

Φ

• Expansion of high load limit

while maintaining almost same emissions levels is possible

• Boundaries of practical
• peration ranges can be

inferred from emissions trends, especially CO

• CO inflection point

correspond to the start of increase in HC and NOx

Thank You