Paper #

Investigation of Effects of Ignition Improver on Ignition Delay Time of Ethanol Combustion with

Rapid Compression and Expansion Machine

Ronnachart Munsin Yossapong Laoonual

Sumrerng Jugjai

King Mongkut’s University of Technology Thonburi (KMUTT)

Masataka Matsuki Hidenori Kosaka

Tokyo Institute of Technology

15th February 2012 Gemini Room, Miracle Grand Hotel, Bangkok, THAILAND

Paper #

Content

1. Background

2. Research methodology

3. Results and discussions

4. Conclusion

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Energy consumption increases every year

Diesel is the largest part of the consumption

Fig. 1 – Trends of transport energy consumption by type of Thailand [Thailand Energy Statistics]

1. Background

Paper #

Among renewable fuels, ethanol is considered as an alternative fuel for diesel engine.

1985 Ethanol buses for public transportation (Sweden)

Bioethanol can substitute a significant percentage of the diesel used for transport.

Fuel and engine research and develop

2006 to

2009

“BioEthanol for Sustainable Transport (BEST)” City buses equipped with CI engines fuelled by commercial ethanol fuel in Europe, Brazil and China

2010 Ethanol buses for public transportation in South Africa and Thailand

1. Background (Continued)

Paper # Fig. 2 - Estimations of λtip and Tspm histories after fuel injection for ethanol [Saitoh and Uchida, 2007, SAE 2007-01-3617]

However, ethanol has poor ignition quality, because of its properties.

Ethanol is difficult in simultaneously achieving suitable concentration and temperature for self-ignition in a spray mixture formation .

(Eq

uiv

ale

nce

ra

tio

at

spra

y t

ip)

Ignition Temp. (Tig)~630 K

λ=1 (stoichiometry)

Tspm < Tig

1. Background (Continued)

(Mea

n t

emp

era

ture

of

spra

y)

Paper #

Two solutions to this problem exist:

1. Engine modifications - spark assistant and dual fuel injection (complicated)

2. Fuel improvement - using “ADDITIVES” (easy and convenient)

Nitrate-based additive was one the most efficient ignition improvers. However, use of nitrate-based improvers has potential for increased corrosion, possibility of explosion, toxicity, wearing and NOx emission.

For this reason polyethylene glycol (PEG) is considered the alternative. Using of polyethylene glycol and nitrate additive resulted in the same ignition delay with no difference in price, but solubility of

PEG becomes problematic at low temperature.

1. Background (Continued)

More recently ED95 is used for CI engines ,

ED95 : 95% hydrous ethanol + 5% Commercial additive (main ignition improver is glycerol ethoxylate)

Cost of additive is still high

Composition of glycerol ethoxylate is not clear

Paper #

Property Biodiesel

[20, 23]

DEE

[20, 25]

Fomula C18.74H34.43O2 C2H5OC2H5

Oxygen content (% weigth) 10.97 21.62

Stoichiometric A/F ratio 13.8 11.13

Viscosity(cP) 3.50@37.8oC 0.23@20oC

Density, g/cc at 20 oC 0.881 0.713

LHV (MJ/kg) 37.388 33.89

Cetane 51.5 >125

Latent heat of vaporization (kJ/kg) n.a. 351.16

Boiling temperature (oC) 182-338 35

Autoignition temperature (oC) 170 160

Table. 1 – The properties of ethanol and ignition improvers

However, ignition and combustion of these ignition improvers have gaps in current understanding.

For this reason, this study investigates the effects of promising ignition improvers and commercial additives on ignition delay and combustion characteristics of ethanol under simulated CI engine conditions, at high injection pressure.

Biodiesel and diethyl-ether (DEE) are expected to improve the ignition quality of ethanol as same as commercial additive, as they have suitable properties for CI engines

Paper #

2. Research methodology

Paper #

Experimental setup

Figure 3 - Schematic diagram of the experiment

RCEM with Flat piston

Bore 100 mm

Stroke 150 mm

CR 8.5

Surrounding conditions

Temperature : Tg 900 K

Pressure : Pg 4.4 MPa

Density :ρg 21 kg/m3

Synthetic air : 20% O2 + 80% Ar

The calorific value of injected fuels is kept constant

Injection conditions

Single hole nozzle diameter

0.24 mm

Injection pressure 90 MPa

Injection durations 3.05-3.5ms

Injection amounts 35.52-36.99 mg

Table. 2 – Experimental conditions 1. RCEM with mixing tank

2. A injection System

3. Data acquisitions

Paper #

Table. 3 Tested fuels

1. Hydrous ethanol with commercial additives: ED95 2. Hydrous ethanol with 5% water (w/o ignition improver): Eh95 3. Hydrous ethanol with 1% glycerol ethoxylate: Eh95+1% glycerol ethoxylate 4. Hydrous ethanol with 5% glycerol ethoxylate: Eh95+5% glycerol ethoxylate 5. Hydrous ethanol with 5% biodiesel: Eh95+5% biodiesel 6. Hydrous ethanol with 5% DEE : Eh95+5% DEE

Fuels

Compositions, %wt

ED95 Eh 95

Eh95+ 1%Glycerol ethoxylate

Eh95+ 5%Glycerol ethoxylate

Eh95+ 5%Biodiesel

Eh95+ 5%DEE

Ethanol 84.36 94.00 93.06 89.30 89.30 89.30

Water 4.44 5.00 4.95 4.75 4.75 4.75

Lauric acid - 1.00 0.99 0.95 0.95 0.95

Ad

dit

ive

s Commercial

additive 11.20 - - - - -

Glycerol ethoxylate - - 1.00 5.00 - - Biodiesel - - - - 5.00 - DEE - - - - - 5.00

Paper #

Time [ms]

0 1 2 3 4

In-c

yli

nd

er p

ress

ure

[M

Pa]

4.0

4.5

5.0

5.5

6.0

SOCSOI

Ignition delay

Pressure recovery point

Injection signal

Ignition delay determination

Fig. 4 – Determination of Ignition delay time by pressure histories and injection signal

Eh9

5

ED

95

Eh9

5+1%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

biod

iese

lEh9

5+5%

DEE

Appar

ent

com

bust

ion

eff

icie

ncy

, %

0

10

20

30

40

50

60

Apparent combustion efficiency

Fig. 5 – Apparent combustion efficiency

Observed apparent combustion efficiencies are similar for each fuel

The different fuels were injected into cylinder with the same heat input.

Paper #

3. Results and Discussions

Paper #

Eh9

5ED

95

Eh9

5+1%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

biod

iese

l

Eh9

5+5%

DEE

Die

sel [

27]

Nea

t eth

anol

[21

]

Ign

itio

n d

elay

, m

s

0.0

.5

1.0

1.5

2.0

2.5

0

Figure 6 - Ignition for tested fuels

Representative of low and high ignition quality ethanol fuel for diesel engines The ignition delay for hydrous ethanol with

commercial improver (ED95) is much shorter than that of hydrous ethanol (Eh95).

However, the ignition delay for hydrous ethanol with commercial improver (ED95) is longer than that of diesel fuel by approximately 75%, but it is considered acceptable for diesel engines

Both 1% and 5% by weight glycerol ethoxylate additives significantly improved ignition quality of the hydrous ethanol, because increasing the number of attack sites for creation of radicals and thermally unstable.

Addition of biodiesel and DEE at 5% by weight has little effect on the ignition delay. Ignition delay times are slightly reduced, explainable by the dependency of local mixture stoichiometry on the oxygen content of fuels.

Ignition delay

Paper #

Eh9

5ED

95

Eh9

5+1%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

glyc

erol

eth

oxyl

ate

Eh9

5+5%

biod

iese

l

Eh9

5+5%

DEE

Die

sel [

27]

Nea

t eth

anol

[21

]

Ign

itio

n d

elay

, m

s

0.0

.5

1.0

1.5

2.0

2.5

0

𝜏 = 10−14𝑒𝑥𝑝 15500

𝑇 𝐶2𝐻5𝑂𝐻 −0.315 𝑂2

−0.78 𝐴𝑟 +0.259 (1)

The global expression for ignition delay time for neat ethanol, Curran et. al. [27] , 1992.

Comparison of the calculated ignition delay for neat ethanol against Eh95, shows that the calculated value is higher than experimental measurements.

This variation can be attributed to the difference in operating conditions

Figure 6 - Ignition for tested fuels

Ignition delay

Paper #

Figure 7 - Example of flame images between 1.4 to 2.1 ms after injection of different fuels taken by high speed camera at 10000 fps

(a) Eh95

(b) ED95

(c) 1%G

(d) 5%G

(e) 5%B

(f) 5%D

1.4 ms 1.5 ms 1.6 ms 1.7 ms 1.8 ms 1.9 ms 2.0 ms 2.1 ms VDO

Paper #

Figure 8 - (a) In-cylinder pressure, (b) heat release rate and (c) cumulative heat release of tested fuels

Eh95+5% glycerol ethoxylate behaves near identical to hydrous ethanol with commercial improver (ED95).

Eh95+1% glycerol ethoxylate, Eh95+5% biodiesel, Eh95+5% DEE and Eh95 are yield diverse data compared to hydrous ethanol with commercial improver (ED95).

In Figure 8 (a) and (c), the peak in-cylinder pressures and cumulative heat release for all tested fuels are similar due to injection at equal calorific value.

Eh95 exhibited the most rapid pressure rise and highest heat release rate.

Eh95+5% glycerol ethoxylate, and (ED95) showed contrary results

Paper #

4. Conclusion

Although the properties of neat biodiesel and DEE are suitable for CI engines, addition of 5% biodiesel and 5% DEE showed insignificant effect on the ignition and combustion characteristics of ethanol.

Hydrous ethanol with 1% and 5% glycerol ethoxylate show promising results compared to hydrous ethanol with commercial additive (ED95).

Hydrous ethanol with 5% glycerol ethoxylate gave a shorter ignition delay time than hydrous ethanol with commercial additive (ED95), and their combustion characteristics are near identical.

Hydrous ethanol with both 1% and 5% glycerol ethoxylate can be

considered as fuels for high compression-ratio CI engines

Paper #

Thank you for your attention