The Optimization Design for Energy Saving of the LPG Dual Fuel Diesel (DDF/LPG) Engine of a Heavy Du

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The Optimization Design for Energy Saving of the LPG Dual Fuel Diesel (DDF/LPG) Engine of a Heavy Duty Truck Yang‐Tai Thomas Lin *1, Horng‐Shing Chiou 2, Li‐Shin Lu3 New Environment Foundation

1

236, Sec. 2, Fuxing S. Rd., 106 Taipei, Taiwan, R.O.C. Department of Electrical Engineering, Taipei Chengshih University of Science and Technology

2

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

3

No.2, Xueyuan Rd., 112 Taipei, Taiwan, R.O.C. *1

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

Abstract Introducing LPG gas into the combustion air intake of a diesel engine acts as an accelerant , promoting the even burning of the diesel fuel , and more complete combustion, resulting in more power being produced and fuel cost savings up to 20% is being achieved through some expensive, modern and sophistical electronic control technology in these few years in Australia,New Zealand,Europe,U.S,Japan and Korea. A much more economical technology by upgrading the early technology of dual‐fuel LPG engines based on a mechanical fumigation system to realized a significant increase in power and fuel cost savings has being developed and presented. The power map and the boost pressure for different loads through 500~3000 engine rpm for both diesel engine and DDF/LPG engine of a Mitsubishi 7545 c.c., 6 cyl. Engine are tested. The results show that the power increase percentage is in proportional to the boost pressure increase rate between the DDF/ LPG engine and the original diesel engine. Since both power and boost pressure are functions of the engine rpm , the fuel consumption of diesel fuel that is proportional to the power is in a function of boost pressure. Therefore , the optimal amount of LPG injection into each cylinder of diesel engine is in a function of boost pressure of the DDF/LPG engine. The boost pressure oriented DDF/ LPG injection controller have been developed and installed on two 11‐ton and 15‐ton refuse trucks and a 35‐ton sandstone trailer respectively. All the three heavy duty DDF/ LPG trucks have run with better performance and 18% fuel cost saving for six months. The cost of the DDF/LPG system of this research is only 5,000 U.S. dollars that is only 1/3 of those of the other modern DDF/LPG Systems.

Keywords DDF/LPG; Combustion; Boost Pressure; Oriented Controller; Optimal Injection of LPG; Low Cost Energy Saving System

Introduction Every diesel combustion burns approximately 75% of the diesel in the chamber; by adding a shot LPG into the combustion chamber it is up to 95%. 30% LPG substitution for a Dutch trucking company resulted in 15% saving on fuel cost per vehicle with an overall return on investment of 1.5 years. There are 7 companies produce LPG dual‐fuel systems and another 6 are developing or produce LPG dual‐fuel conversion systems in the world. Two automotive research institutes, in India and China, are engaged in dual‐fuel engine developments (Seisler, 2010). Mixing a shot of LPG with the air through the turbocharger improves the brake specific fuel consumption (BSFC) or the thermal efficiency of the diesel engine. And cost saving up to 20% is been achieved through revamping a DDF/LPG system with ECU and LPG injections near the air intake port of each cylinder of the engine for most heavy duty diesel engines of Euro III and Euro IV emission levels, besides 9~25% CO2 reduction and smoke and particulate emissions decrease significantly; to 40% to 60% by some claims.

Four DDF/CNG systems from Japan, USA and New Zealand have been revamped on the diesel buses to conduct the engine performance tests through chassis dynamometer and the off‐road tests on the high way and in sown town Taipei City, Taiwan, R.O.C. for several research projects since 1998 (Lin and Liang, 1998; Lin and Huang, 1998; Lin, 1999; Hsu et al., 2001).

The DDF/CNG Bus Project was terminated due to refuelling station safety issues in districts in highly populated metropolitan city. However, 60 LPG

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refuelling stations for taxi have been built in Taiwan.

Therefore the DDF/CNG experiences are being applied to develop DDF/LPG systems for heavy duty trucks to restore the weakening LPG refuelling station industry here. The turning table of the DDF/CNG ECU which evaluate between signal RPM (Engine) and TPS (Accelerator position) active axle X, Y be axle Y signal TPS, axle X signal RPM can be multiplied by a factor of 0.614 (Wobble index of CNG=12735 kcal/Nm3 divided by Wobble index of LPG 20755 kcal/Nm3) to DDF/LPG system. The evaporator of CNG should be changed to LPG evaporator too.

DDF/LPG system is shown in Fig. 1.

Experiment Device and Method

Engine The experiment is conducted on Mitsubishi 6D16‐1AT six‐cylinder turbocharger intercooled Diesel engine of which the main technical parameters 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 intercooled after ail intake is maintained by the cooling control unit at no higher the 50℃.

TABLE 1 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

FIG. 1 SCHEMATIC DIAGRAM OF EXPERIMENT SETUP FOR THE DDF/LPG SYSTEM.

Experiment Results and Analysis Experiment Results The ESC 13 mode test on the Diesel engine’s emissions and fuel consumption has been conducted at the Taiwan EPA authorities Automotive Research and Testing Center (ARTC). The power map of DDF and Diesel engine is shown in Fig. 2. A high pressure turbocharger is added to the DDF engine to form a regulated 2‐stage turbocharger system for raising the boost pressure and torque in low rpm from 500 to 1000.

800

180

700 DDF with LP TURBO

160

600 DDF with HP TURBO

Experiment Equipment

56

120 400

100 80

300

Power (kW)

Torque (N.m )

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 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; LPG 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

140

500

60 200

Diesel with HP TURBO

100

0

40 20

0

0 500 1000 1500 2000 2500 3000 3500

FIG. 2 POWER MAP OF DDF/LPG AND DIESEL ENGINE WITH A MODIFIED REGULATED 2‐STAGE TURBOCHARGER SYSTEM.

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800

700

600

500

P

P P

DSL

DSL

1

DSL

0

0.8

300

0.6 DDF boost pressure

200

0.4 Diesel boost pressure

0

DDF

DDF

P

400

0

P

0

Diesel torque

100

DDF

1

1.0

0.2

r1/r0-1 Boost Pressure (kg/cm2 )

Torque (N.m )

P

Power

DDF torque

0 500 1000 1500 2000 2500 3000 3500

r r r=R rpm/3000rpm 0

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

The heating value of Diesel, H DSL , is assumed to be 10,000 kcal/kg, and the heating value of LPG, H DME , is assumed to be 6,900 kcal/kg, and H LPG   H DSL , where  0.69 . Then, P1DDF  m DSL  H DSL  m DSL  H DSL P0DSL  m DSL  H DSL (1) P1DDF P0DSL

 1  

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

T DDF / (1  B DDF )  const. and 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

In Fig. 4, the Diesel engine is running at a speed of R0 rpm and set r0 = R0/3000 rpm, the LPG injection mass flow rate m LPG  m DSL , where m DSL is the mass flow rate of Diesel and  is the ratio of LPG amount to Diesel fuel. When the LPG 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.

FIG. 4 POWER AND ENGINE SPEED RELATION OF THE DDF AND ORIGINAL DIESEL ENGINE.

FIG. 3 TORQUE AND BOOST PRESSURE MAP OF DDF/LPG AND DIESEL ENGINE WITH A REGULATED 2‐STAGE TURBOCHARGER SYSTEM.

Fig. 2 reveals that the maximum load power of DDF/LPG engine is averagely 23% higher than the original Diesel engine through the rpm range from 900 to 2700. The BSFC (in g/hp‐hr unit) of DDF/LPG engine is about 16% lower than the original engine or the fuel cost savings is up to 20%, and accordingly CO2 exhaust is reduced by 20%. The overall LPG displacement mass rate of the DDF/LPG fuel is about 18%. The torque and boost pressure map of DDF/LPG and Diesel engine is shown in Fig. 3. The maximum torque of DDF engine is 817 Nm which is 27% higher than 642 Nm of Diesel engine at engine speed of 1710 rpm. When rpm is raised up to 2700, the maximum load torque of DDF engine is only 13% higher than that of Diesel engine. Averagely, the torque increase is 20% between the DDF and original Diesel engine through the range from 900 to 2700 rpm.

r

1

P0DSL



P0DDF P1DDF r1   P0DSL P0DDF r0

1   

T0DDF r1 r1   T0DSL r0 r0

Therefore 1  1  B0DDF      1  B0DSL 

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

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

P0DDF P0DSL



P1DDF P0DDF r0   P0DSL P1DDF r1

P DDF r r  1 DSL  0  0 (3) r1 r1 P0  1  B1DDF   DSL  1  B0

 r0    r1

The energy saving rate s  1

m DME 

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 in Fig. 2.

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

   0.1  0.28B 

Opt m LPG  m DSL 0.1  0.21B D

1 (4) BSFCr

The r1/r0 is measured at different load conditions and rpm. The relation between r1/r0 versus r0 is shown in Fig. 3.

Optimization Design for a LPG Injection Controller The boost pressure of the original Diesel engine BDSL and that of the DDF/LPG engine BDDF is expressible in the form as

 m DSL

D

( for B D  0.3) ( for B D  0.3)

Development of a Boost Pressure Oriented LPG Mass Rate Injection Controller The boost pressure oriented LPG mass rate injection controlled DDF/LPG system is shown in Fig. 5. A pedal pressure regulator and two LPG air relays are fixed on the DDF/LPG system as shown in Fig. 6 and Fig. 7, respectively.

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

FIG. 5 BOOST PRESSURE ORIENTED LPG MASS RATE INJECTION CONTROLLED DDF/LPG SYSTEM.

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

   (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  1  B DSL m DSL

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

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FIG. 6 SCHEMATIC DIAGRAM OF LPG AIR‐RELAY.

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(A) LPG FUEL TANK AND IN REFUELLING OF THE TRAILER

FIG. 7 SCHEMATIC DIAGRAM OF PEDAL PRESSURE REGULATOR.

Appications The boost pressure oriented DDF/LPG injection controller have been developed and installed on two 11‐ton and 15‐ton refuse trucks and a 35‐ton sandstone trailer respectively, as shown in Fig. 8 and Fig. 9.

(B) THE BOOST PRESSURE ORIENTED CONTROLLER OF DDF/LPG SYSTEM ON THE TRAILER FIG. 9 A 35‐TON DDF/LPG SANDSTONE TRAILER.

(A) DIESEL REFUSE TRUCK

All these heavy duty DDF/LPG trucks have run with better performance and 15~20% fuel cost saving for six months. The cost of these DDF/LPG system is only U.S. $5,000 that is only 30~40% of those of the other modern DDF/LPG systems in the world market.

Conclusions The DDF/LPG system using sophistical electronic control unit has been tested to derive a boost pressure oriented equation for optimal LPG injection to Diesel engine. The much more lower cost DDF/LPG system using boost pressure as an actuating force to control the LPG injection amount into the Diesel engine has be developed. All the three DDF/LPG systems developed by this research have been installed on 11‐ton, 15‐ton and 35‐ton refuse trucks and sandstone trailer respectively, and have run successfully for six months.

(B) DDF/LPG DUAL FUEL SYSTEM INSTALLED ON TRUCK FIG. 8 A 15‐TON TAIPEI CITY DDF/LPG REFUSE TRUCK.

ACKNOWLEDGMENT

The authors wish to express gratitude to National

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Science Council of Taiwan, R.O.C. for financial support on engine tests. The authors also wish to give thanks to Dr. Stephen Shu‐Hung Shen, Minister of Environmental Protection Administration of Taiwan, R.O.C. for his conceptual inspirations and long time contact advices to this study.

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Diesel Engines”, Report of Clean Fuels Consulting,

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Brussels, Belgium, April 2010.

Lin, Y.T., “Fleet tests of the DDF.CNG fuelled bus”, Report

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