The Optimal Design of DME Injection for NOx Reduction of the DME Dual Diesel (DDF/DME) Engine on a H

International Journal of Engineering Practical Research (IJEPR) Volume 3 Issue 4, November 2014 www.seipub.org/ijepr doi: 10.14355/ijepr.2014.0304.05

The Optimal Design of DME Injection for NOx Reduction of the DME Dual Diesel (DDF/DME) Engine on a Heavy Duty Truck Li‐Shin Lu*1, Horng‐Shing Chiou 2, Shah‐Rong Lee1, Chao‐Wen Yen1, Yang‐Tai Thomas Lin 3 Department of Mechanical Engineering, Taipei Chengshih University of Science and Technology No.2, Xueyuan Rd., 112 Taipei, Taiwan, R.O.C. 1

Department of Electrical Engineering, Taipei Chengshih University of Science and Technology No.2, Xueyuan Rd., 112 Taipei, Taiwan, R.O.C. 2

New Environment Foundation, 236, Sec. 2, Fuxing S. Rd., 106 Taipei, Taiwan, R.O.C.

3

*1

lslu@tpcu.edu.tw; 2hschiou@tpcu.edu.tw; 1srlee@tpcu.edu.tw; 1cwyen@tpcu.edu.tw; 3yttlin36@ms48.hinet.net

Abstract Introducing DME gas into the combustion air intake of a engine acts as an accelerant, promoting more complete combustion, and resulting 27.3% NOx emission reduction has been achieved using the DDF/DME control system. The ESC 13 Mode tests of a Mitsubishi 7545 c.c., 6‐cyl. Diesel engine with a DDF/DME system are conducted. The optimal amount of the DME injection into each cylinder of the Diesel engine for NOx reduction purpose is derived as function of the boost pressure at the manifold. Experimental results show that the boost pressure is linear to the engine rpm for 50% load of DDF/DME engine. This line is parallel to the boost pressure – engine rpm line for 50% load of DDF/LPG engine. A boost pressure oriented LPG injection controller has been developed to revamp on the Diesel engine of a 15‐ton Taipei City refuse truck. The DDF/LPG heavy duty truck has been running 8 months with 18% fuel saving rate and 32% smoke reduction rate. The boost pressure oriented DME injection controller for NOx reduction purpose is being fabricated and tested on the same heavy duty refuse truck. The average substitution of DME to Diesel is 27.5 % by mass fraction. The cost of DDF/DME system is only 5,000 USD per set. An efficient DDF/DME system is important to the reduction of the NOx emissions of the 120,000 Euro II and Euro III standard heavy duty trucks and the set‐up of DME for transportation fuel industry in future Taiwan.

Keywords DDF/DME System; Optimal Design of DME Injection; Boost Pressure Oriented Controller; Reduction of Nox Emissions

Introduction Physical Properties of Diesel, LPG and DME, and the Combustion Systems Dimethyl Ether (DME) is a clean and economical

alternative fuel which can be produced from various resources as natural gas, coal or biomass through synthesis gas. The properties of DME are similar to those of LPG and it can be used for various fields: power generation fuel, transportation fuel, home fuel, etc. The physical properties of Diesel, LPG and DME are shown in Table 1.

TABLE 1 PHYSICAL PROPERTIES OF DME AND OTHER FUEL.

Properties Chemical formula Boiling point (oC) Liquid density (g/cm3 @ 20oC) Specific gravity of gas vs. air Vapor pressure (atm) Cetane number Net calorific value (kcal/kg)

DME

LPG

Diesel

CH3OCH3

C3H8

‐25.1

‐42.0

180~370

0.67

0.54

0.84

1.59

1.76

6.1

5.75

55~60

0

40~55

6,900

12,368

10,000

From Table 1, DME similar to LPG, can rapidly blend with air to form a combustible mixture due to very low boiling point and high evaporation pressure. The pressures of DME and LPG are also similar, around 6 atm, therefore they are suitable for vehicle fuel use due to very low pressure of storage tank compared to 200 atm of CNG tank. DEM, with a lower self‐ignition temperature, high cetone number and short ignition delay period, is prone to compression ignition of Diesel engine. Pure DME, lower in heating value, can cause lower engine output. However, engines fuelled

by Diesel blended with DME (DDF/DME) can combine

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with both the high output and lower NOx emissions.

Since DDF/DME combustion systems are similar to DDF/LPG systems which are very well developed and intensively studied, the DDF/LPG engine experiences are vital to this research.

emissions laws of composite combustion mode of DME and Diesel are studied and the experimental results show that NOx and smoke emissions are reduced significantly for a 2,000 c.c., 4‐cyl. light duty Diesel engine (Duan et al., 2012).

DDF/LPG Engine Technologies are Improving and Becoming More Widespread for On‐road Applications

Experiment Device and Method

Contemporary gaseous dual‐fuel‐Diesel (DF) engines have been under development in Europe and the U.S. since the early 1980s. A 2010 inventory by Clean Fuels Consulting of companies engaged in dual‐fuel gaseous/Diesel engines and vehicles – natural gas and liquid petroleum gas (LPG) – identified at least 34 different companies engaged in some form of development, production and sale of these emerging technologies (Seisler, 2010). There are 20 companies actively engaged in developing, producing and selling dual‐fuel gaseous/Diesel conversion systems. Seven of these produce LPG dual‐fuel systems and six are developing or produce both natural gas and LPG dual‐fuel conversion systems. The retail price of a DDF/LPG system for heavy duty truck is around 30,000 U.S. dollars per truck. 30% LPG substitution for a Dutch trucking company results in 15 savings on fuel costs per vehicle with an overall return on investment of 1.5 years.

The experiment is conducted on Mitsubishi 6D16‐1AT six‐cylinder turbocharger intercooled Diesel engine of which the main technical parameters are shown in Table 1. During the experiment, the fuel temperature is controlled by the fuel temperature control device at no higher than 40℃. The temperature intercools after ail intake is maintained by the cooling control unit at no higher the 50℃.

This research has developed 3 boost pressure oriented DDF/LPG systems which are revamped on a 15‐ton Taipei City refuse truck, a 11‐ton New Taipei City refuse truck and a 35‐ton sandstone trailer truck, respectively. All these 3 DDF/LPG heavy duty trucks run 8 months with 18% fuel saving rate and 32% smoke reduction rate (Lin, 2014). The cost of the boost pressure oriented LPG injection controlled DDF/LPG system (25% LPG substitution) is around 5,000 U.S. dollars per truck.

Experiment Equipment

Engine

TABLE 2 THE MAIN TECHNICAL PARAMETERS OF THE DIESEL ENGINE.

Items Type Number of cylinder Displacement The number of injector holes Compression ratio Rated power Rated speed Maximum torque Year of make

Parameters Six cylinder with turbocharger 6 7545 c.c.

6 17.5:1 212 HP/2800 rpm 3000rpm 434 ft‐lb/1600 rpm 1996

DDF/DME Related Experiments Review Due to its good fuel economy and adaptability, Diesel engines are widely used. However, high NOx emissions and smoke formation are always the main weak points and problem hard to deal with. To explore strategies to reduce NOx emissions from compression ignition engines has been conducted through a mixed mode combustion process utilizing a fumigated fuel and a pilot injection of Diesel fuel on a light duty engine. An approximately 20% reduction in NOx emissions is observed up to 35% DME energy equivalent (Chapman, 2008). Combustion and

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FIG. 1 SCHEMATIC DIAGRAM OF EXPERIMENT SETUP FOR ELECTRONIC DME INJECTION CONTROLLED DDF/DME SYSTEM.

The main equipment and instruments used for the experiment include: a GO Power DT‐1000 water brake dynamometer with maximum power 500 HP, max. torque 1000 ft‐lb and max. speed 4000 rpm, a Beltone Technology BT‐2000, CO, HC, CO2, O2 and NOx

International Journal of Engineering Practical Research (IJEPR) Volume 3 Issue 4, November 2014 www.seipub.org/ijepr

emission analyser, and a Horiba Okuda DSM‐240 opacity smoke meter. This experiment uses a dual fuel supply system: diesel going over a fuel consumption instrument though low pressure, high pressure pump into the injection nozzles; DME from the tank regulated through the pressure regulating valve to about 0.2 MPa, being led into the intake port near valve for rapid vaporization and mixing with air to form a premixed gas, which then enters the cylinder.

The schematic of the experiment equipment setup for the electronic DME injection controlled DDF/DME system is shown in Fig. 1.

Experiment Results and Analysis The ESC 13 Mode tests on the Diesel engines and Diesel/DME DDF engines emissions, torque, power mass flow, and boost pressure have been conducted at Taiwan EPA authorized Automotive Research and Testing Center (ARTC) and by this research are shown in Table 3 and Table 4 referred to Fig. 2.

The boost pressure vs. engine speed curves under various loads for Diesel, DDF/LPG and DDF/DME engines, respectively, are shown in Fig. 3.

8%

9%

2

100

8

9 10 11 12 13

2100 2500 2500 2500 2500

0.17 0.62 0.22 0.46 0.33

0 0 0 0 0

110 400 100 300 200

44 190 47 143 95

0.35 0.75 0.50 0.70 0.70

182 876 209 610 410

0.028 0.068 0.032 0.020 0.045

17 39 19 50 40

*A: Engine speed (rpm), B: Mass flow rate of Diesel (kg/min.), C: Mass flow rate of DME (kg/min.), D: Torque (lbf‐ft), E: Power (hp), F: Boost pressure (kg/cm2).

TABLE 4 EUROPEAN STATIONARY CYCLE (ESC) TEST OF DIESEL/DME DDF ENGINE.

Mod e No. 1 2 3 4 5 6 7 8 9 10 11 12 13

B C A (kg/min (kg/min (rpm) ) ) 600 0.015 0 1720 0.40 0.08 2180 0.20 0.10 2160 0.23 0.12 1750 0.20 0.06 1780 0.28 0.10 1760 0.12 0.04 2130 0.48 0.08 2200 0.12 0.08 2530 0.56 0.10 2580 0.14 0.10 2550 0.36 0.14 2550 0.24 0.12

D (lbf‐ ft) 35 470 240 350 250 380 130 450 120 415 110 320 220

F E (kg/cm2 (hp) ) 4 0.02 154 0.72 100 0.55 144 0.6 81 0.35 129 0.55 44 0.20 183 0.75 50 0.4 200 0.75 54 0.55 155 0.75 107 0.72

NOx CO HC (ppm (%) (ppm) ) 52.2 0.005 3.6 590 0.043 35.5 298 0.069 78.3 348 0.143 37.7 276 0.067 43.5 493 0.121 79.8 202 0.073 83.2 620 0.086 45.2 143 0.082 110 673 0.112 110 166 0.093 120 484 0.159 50.2 330 0.085 80.6

8%

10

2 Min. 0.8

10%

75

6

50

5

4

3

9

7

2 Min.

5%

13 10%

5% 25

12 10%

5%

0.7

5% Boost Pressure (kg/cm2 )

Load (%)

5%

2 Min.

5%

11

0

1

0.5

75% 75% 75%

0.4 0.3

50% 50% 50% DDF/LPG

2 Min.

0.2

DDF/DME Diesel

25% 25% 25%

0.1

15% 0

0.6

100% 100% 100%

1700

Idle (600 rpm)

2100

0

2500 2850 Max. Eng. speed

Engine Speed (rpm)

FIG. 2 SCHEMATIC DIAGRAM OF EUROPEAN STATIONARY CYCLE (ESC) 13 MODE. TABLE 3 EUROPEAN STATIONARY CYCLE (ESC) TEST OF ORIGINAL DIESEL ENGINE.

B C Mode A (kg/min (kg/min No. (rpm) ) ) 1 600 0.015 0 2 1700 0.41 0 3 2100 0.27 0 4 2100 0.38 0 5 1700 0.22 0 6 1700 0.32 0 7 1700 0.13 0 8 2100 0.51 0

D (lbf‐ ft) 35 460 220 330 230 350 120 440

F E (kg/cm2 (hp) ) 4 0.02 149 0.70 88 0.50 113 0.70 74 0.30 113 0.53 39 0.15 176 0.75

NOx CO HC (ppm (%) (ppm) ) 52.2 0.005 3.6 890 0.022 11 402 0.023 28 639 0.009 43 360 0.021 22 620 0.005 21 240 0.023 10 880 0.044 23

1700

2100 Engine Speed (rpm)

2500

2850

FIG. 3 BOOST PRESSURE VS. ENGINE SPEED UNDER VARIOUS LOADS.

From Fig. 3, under 50% load, the boost pressure is linear with engine rpm for Diesel, DDF/LPG and DDF/DME engines. The NOx emissions vs. engine speed under various loads for Diesel and DDF/DME engines is shown in Fig. 4.

From Fig. 4, the NOx reduction effect of DDF/DME engine to original Diesel engine is most significant under 50% load for all engine rpm. The DME substitution rate for all 13 Mode test of the DDF/DME engine is calculated as shown in Table 5. The average DME substitution rate is 27.5% in weight, and 18.43% in energy equivalent.

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TABLE 7 EMISSIONS IMPROVEMENT FROM DIESEL TO DDF/DME ENGINE.

1000 900

Item Engine Diesel (ESC)

100%

800 Diesel DDF/DME

NOx (PPM )

CO

HC

PM

BSFC

0％

0％

0％

0％

0％

Expected 11.7 ‐194.3％ ‐174.3％ DDF/DME 27.3％ (ESC) ％ But 2.662＜10 But 0.491＜1.3 50％*

700 600

NOx

75% 100%

* DDF/LPG and DDF/DME engines are similar in ARTC U.S. TRANSIENT test of PM: from Diesel of 0.42 drop to DDF/DME of 0.21 ( g / hp  hr ).

500 75% 400 50%

200

Derivation of the Equation of DME Injection for DDF/DME Engine

50% 25% 25%

In Fig. 5, the Diesel engine is running at a speed of R0 rpm and set r0 = R0/3000 rpm, the DME injection mass flow rate m LPG  m DSL , where m DSL is the mass flow

100 0

1700

2100 Engine Speed (rpm)

2500 2850

FIG. 4 NOX EMISSIONS VS. ENGINE SPEED UNDER VARIOUS LOADS. TABLE 5 THE SUBSTITUTION RATE FOR ALL 13 MODE TEST OF DDF/DME ENGINE.

Mode

1 2 3 4 5 6 7 8

rate of Diesel and  is the ratio of LPG amount to Diesel fuel. When the DME fuel is injected into the Diesel engine, the engine speed is raised to R1 rpm or r1 = R1/3000 rpm, and the power of Diesel engine P0DSL is also raised to P1DDF of DDF engine.

9 10 11 12 13 Average

Substitution 0 17 33 34 23 26 25 14 40 15 40 28 33 rate % % % % % % % % % %1 % % %

27.5 %

The average values of Mode 3 emissions and BSFC of Diesel and DDF/DME engines are shown in Table 6.

From Table 6, the ESC average values are about 5% above or below Mode 3 values of emissions and BSFC for both Diesel and DDF/DME engines.

Power

300

P

DDF

P

DDF

1

P

DDF

0

P P

DSL

D SL

1

P

D SL

0

TABLE 6 EMISSIONS AND BSFC OF ESC AVERAGED VALUE AND MODE 3 VALUE IN DIESEL AND DDF/DME ENGINES.

Euro III HD Diesel NOx Engine Emission 5.0 Standard Diesel 5.04 (ESC Average) Diesel 4.86 (Mode 3) DDF/DME 3.66 (ESC Average) DDF/DME 3.53 (Mode 3)

CO

HC

BSFC

10.0

1.3

r r r= R rp m /3 0 0 0 rpm 0

0.905

0.179

185.31

FIG. 5 POWER AND ENGINE SPEED RELATION OF THE DDF AND ORIGINAL DIESEL ENGINE.

0.962

0.202

182.00

2.662

0.491

163.61

2.830

0.554

160.69

The heating value of Diesel, H DSL , is assumed to be 10,000 kcal/kg, and the heating value of DME, H DME , is assumed to be 6,900 kcal/kg, and H LPG   H DSL , where  0.69 . Then,

Unit: g / hp  hr

P1DDF  m DSL  H DSL  m DSL  H DSL

Emissions improvement from Diesel to DDF/DME engines is shown in Table 7. From Table 7, the NOx emission improvement for DDF/DME to Diesel engine is 27.3%. The CO and HC emissions increase for about 200% from Diesel to DDF/DME engine. However, the DDF/DME emissions still do not exceed the Euro III heavy duty Diesel engine standard.

P0DSL  m DSL  H DSL

92

r

1

P1DDF P0DSL

 1   (1)

Since P1DDF  T1DDF  r1 and P0DSL  T0DSL  r0 , where T1DDF is the torque of DDF engine in running at engine

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speed r1, and T0DSL is the torque of Diesel engine at engine speed r0.

From Table 3 and Table 4, it can be found that for both Diesel and DDF engines, the torque T is in proportional to turbocharged pressure that is equal to the atmospheric pressure plus the boost pressure, B, T DDF / (1  B DDF )  const. i.e. and

computation has been done. By eliminating the exp[ar] term, the boost pressure of the Diesel engine, BDSL, is expressible as B DSL  1 

From Equation (5), 1  ln  1  B DSL r  a

T DSL / (1  B DSL )  const. . Substituting these equations into Equation (1), it yields P1DDF P0DSL



T1DDF r1  1  B1DDF   T0DSL r0  1  B0DSL

 r1    r0

Or P1DDF P0DSL



P0DDF P0DSL

1   



P1DDF P0DDF



r1

r0

T0DDF r1 r1   T0DSL r0 r0

Therefore 

1  1  B0DDF    1  B0DSL 

   r1       1 (2)    r0 

BSFCr 

P0DDF P0DSL



P1DDF P0DDF r0 P1DDF r0 r0      P0DSL P1DDF r1 P0DSL r1 r1

 1  B1DDF   DSL  1  B0

 r0   r (3)  1

The energy saving rate s  1

1 (4) BSFCr

   (7)

Trying a = 2.233, r and BDSL relation is formed as r  0.319  0.667 B DSL

Since r1/r0 is also linear with r, therefore, Equation (2) can be expressed as



m 1 kB DDF   DME DSL  1 B m DSL

The injection rate of DME, m DME , becomes as m DME 

2

The BSFC ratio of the DDF engine to original Diesel engine is then

1 1  B DDF   k

km DSL B DDF (1  B DSL )

 k1  B DSL  B D (8)

where k1[BDSL] can be obtained from the original Diesel engine’s power map.

By linearing Equation (8) and extending to all range of acceleration position and rpm, the optimal mass Opt injection rate of DME, m DME , can be expressed as



Opt m DME  m DSL c1  c2 B DDF



(9)

where the constants c1 and c2 are obtained from experiments.

Development of a Pressure Oriented DME Mass Rate Injection Controller to Install on a 15-Ton Freight Truck

The r1/r0 is measured at different load conditions and rpm.

The boost pressure of the original Diesel engine BDSL and that of the DDF/DME engine BDDF are expressible in the form as B DSL  1  exp  ar  (5)

And B DDF  1  k exp  ar  (6)

where exp[ar] is the exponential function of rpm, a and k are constants evaluated at each rpm from the measured boost pressure and the curve fitting

FIG. 7 SCHEMATIC DIAGRAM OF DME AIR‐RELAY.

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DDF/DME system are conducted and the NOx emissions reduction of 27.3% as the DDF/DME system is utilized on the Diesel Engine. The boost pressure oriented controller optimal amount of the DME injection into each cylinder of the Diesel engine has been developed in this research. The cost of this newly invented and efficient DDF/DME system is about 20% to those of the electronic type DDF/DME systems that have been widely sold in the world market. The DME substitution rate is 27.5% by mass fraction and this is important to the set‐up of DME for transportation fuel industry in future Taiwan.

The boost pressure oriented DME mass rate injection controlled DDF/DME system is shown in Fig. 6. Two air relays are fixed on the DDF/DME system as shown in Fig. 7.

The DDF/DME dual fuel system installed on a 15‐ton freight truck is shown in Fig. 8. The DDF/DME heavy duty truck is running in the street of Taipei City, Taiwan.

ACKNOWLEDGMENT

The authors wish to express gratitude to EPA and National Science Council of Taiwan, R.O.C. (Grant NSC 102‐EPA‐F‐010‐001) for financial support on engine tests.

REFERENCES

FIG. 6 BOOST PRESSURE ORIENTED DME MASS RATE INJECTION CONTROLLED DDF/DME SYSTEM.

Chapman, Elana M., “NOx Reduction ‘Strategies’ for Compression Ignition Engines”, The Pennsylvania State University Ph.D. Dissertation, 2008.

Duan, Junfa, Sun, Yongsheng, Yang, Zhenzhong, and Sun, Zhiqiang, “Combustion and Emissions Characteristics of Diesel Engine Operating on Composite Combustion Mode of DME and Diesel’, Proceeding of 2012 International Conference on Mechanical Engineering and Material Science (MEMS 2012).

Lin, Yang‐Tai T., “The Strategic Energy Planning on Use of Biogas for Fuelling Heavy Duty Trucks in Taiwan”, Renewable Energy and Power Quality Journal, ISSN

FIG. 8 DDF/DME DUAL FUEL SYSTEM INSTALLED ON A 15‐ TON TRUCK.

Conclusions The ESC 13 Mode tests for the emissions of a Mitsubishi 7454 c.c., 6‐ cyl. Diesel engine with a

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2172‐038x, No. 12, April 2014.

Seisler, J. M., “A Strategic Roadmap to Market Development of Certified Heavy Duty Gausses Fuel (Methane/LPG) – Diesel Engines”, Report of Clean Fuels Consulting, Brussels, Belgium, April 2010.