A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

US10 Capable Prototype Volvo 

MG11 Natural Gas Engine 

Development: Final Report 

December 16, 2003 — July 31, 2006 

C. Tai and T. Reppert 

Mack Trucks, Inc. 

Hagerstown, Maryland 

J. Chiu 

Southwest Research Institute 

San Antonio, Texas 

L. Christensen, K. Knoll, and J. Stewart 

Sturman Industries 

Woodland Park, Colorado 

Subcontract Report 

NREL/SR-540-40756 

October 2006 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
US10 Capable Prototype Volvo 

MG11 Natural Gas Engine 

Development: Final Report 

December 16, 2003 — July 31, 2006 

C. Tai and T. Reppert 

Mack Trucks, Inc. 

Hagerstown, Maryland 

J. Chiu 

Southwest Research Institute 

San Antonio, Texas 

L. Christensen, K. Knoll, and J. Stewart 

Sturman Industries 

Woodland Park, Colorado 

NREL Technical Monitor: A. Williams 

Prepared under Subcontract No. ZCI-4-32050-01 

Subcontract Report 

NREL/SR-540-40756 

October 2006 

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
This publication was reproduced from the best available copy 

Submitted by the subcontractor and received no editorial review at NREL

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TABLE OF CONTENTS 

Page

EXECUTIVE SUMMARY ............................................................................................................ 1 

1.0 INTRODUCTION .............................................................................................................. 2 

1.1 Project Objective............................................................................................................. 3 

2.0 TECHNICAL DISCUSSIONS/RESULTS......................................................................... 4 

2.1 Engine Description.......................................................................................................... 4 

2.1.1 Engine Breathing .................................................................................................... 5 

2.1.1.1 Intake Manifold................................................................................................... 5 

2.1.1.2 Exhaust System and Turbocharger ..................................................................... 6 

2.1.1.3 EGR System........................................................................................................ 7 

2.1.2 Engine Ignition System........................................................................................... 8 

2.1.3 Engine Pistons......................................................................................................... 9 

2.1.4 Engine Control System ......................................................................................... 10 

2.1.5 HVA System......................................................................................................... 10 

2.2 Engine Development..................................................................................................... 12 

2.2.1 Test Cell Description ............................................................................................ 12 

2.2.2 Engine Calibrations............................................................................................... 14 

2.2.3 Test Points............................................................................................................. 14 

2.2.4 Problems ............................................................................................................... 16 

2.3 Valve Timing Sweeps................................................................................................... 22 

2.3.1 Preliminary Valve Timing Sweeps....................................................................... 22 

2.3.2 Valve Timing Sweeps........................................................................................... 23 

2.3.2.1 Full Timing Sweeps.......................................................................................... 24 

2.3.2.2 Reduced Timing Sweeps................................................................................... 26 

2.3.3 Final Calibration ................................................................................................... 28 

2.4 Baseline Testing............................................................................................................ 30 

2.5 Results Analysis............................................................................................................ 31 

2.5.1 Baseline Efficiency ............................................................................................... 31 

2.5.2 HVA Efficiency .................................................................................................... 33 

2.5.3 Optimized Natural gas Efficiency......................................................................... 33 

2.5.4 Diesel Efficiency................................................................................................... 34 

2.5.5 Efficiency Comparison ......................................................................................... 35 

3. SUMMARY AND CONCLUSIONS ................................................................................... 42 

 iii
LIST OF TABLES 

Page

Table 1. Average Gas Composition and Standard Deviation for Development Work................ 13 

Table 2: Data Recorded ............................................................................................................... 13 

Table 3: Steady State Test Points................................................................................................. 15 

Table 4. Reduced Valve Timing Matrix ...................................................................................... 26 

Table 6. Efficiency and Emissions Results.................................................................................. 29 

Table 7. Operational Settings....................................................................................................... 29 

Table 8. Before Catalyst Emissions Results ................................................................................ 30 

Table 9. Baseline Test Conditions ............................................................................................... 31 

Table 10. Baseline Efficiency Results ......................................................................................... 32 

Table 11. HVA Efficiency Results .............................................................................................. 33 

Table 12. E7GT Efficiency Results ............................................................................................. 34 

Table 13. Diesel Efficiency.......................................................................................................... 35 

Table 14. Efficiency Comparison ................................................................................................ 37 

 iv
LIST OF FIGURES 

Page

Figure 1. End Fill Intake Manifold ................................................................................................ 5 

Figure 2. Center Fill Intake Manifold............................................................................................ 6 

Figure 3. External Wastegate......................................................................................................... 7 

Figure 4. Low Pressure EGR Loop................................................................................................. 8 

Figure 5. Engine Ignition System ................................................................................................... 9 

Figure 6. Piston Designs, Left – 10.25:1 CR, Right – 14.3:1 CR................................................. 10 

Figure 7. Sturman HVA System .................................................................................................. 11 

Figure 8. Sturman Valve Drive Module (VDM) ......................................................................... 11 

Figure 9. Hydraulic Pump Cart for the HVA System.................................................................. 12 

Figure 10. 22-Mode Steady State Test Points.............................................................................. 16 

Figure 11. 16 Steady State Modes Tested.................................................................................... 16 

Figure 12. Broken Intake Valve Head on Cylinder 3 .................................................................. 17 

Figure 13. Valve Head Embedded in the Piston.......................................................................... 18 

Figure 14. Marks on the Piston from Valve/Piston Collisions .................................................... 19 

Figure 15. Foreign Material on the Number One Piston ............................................................. 20 

Figure 16. Excessive Valve Wear................................................................................................ 21 

Figure 17. Oscilloscope Picture Showing an Early Intake Valve Opening Command ............... 22 

Figure 18. Preliminary Testing for Late and Early IVC .............................................................. 23 

Figure 19. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load Varying Exhaust Valve 

Opening................................................................................................................................. 24 

Figure 20. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load Varying Exhaust Valve 

Closing .................................................................................................................................. 25 

Figure 21. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load Varying Intake Valve 

Opening................................................................................................................................. 25 

Figure 22. Full Timing Sweeps Test Points................................................................................. 26 

Figure 23. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load Varying Exhaust Valve 

Opening................................................................................................................................. 27 

Figure 24. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load Varying Exhaust Valve 

Closing .................................................................................................................................. 27 

Figure 25. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load Varying Intake Valve 

Opening................................................................................................................................. 28 

Figure 26. Valve Lift Profile for the HVA system and a Cam .................................................... 32 

Figure 27. 13-Mode Weighted Efficiencies................................................................................. 38 

Figure 28. Efficiencies at 1250 rpm............................................................................................. 39 

Figure 29. Efficiencies at 1600 rpm............................................................................................. 39 

Figure 30. Efficiencies at 1950 rpm............................................................................................. 40 

Figure 31. HVA System Efficiency Improvement over a Cam System ...................................... 40 

Figure 32. HVA System Efficiency Improvement over a 2010 Diesel Engine ........................... 41 

 v
EXECUTIVE SUMMARY 

The objective of this project is to develop a low emissions natural gas engine. The emission 

targets for this project are 0.27 g/kW-hr (0.2 g/bhp-hr) of NOx and 0.013 g/kW-hr (0.01 g/bhphr) of particulate matter. To meet the objective, a chemically correct combustion 

(stoichiometric) natural gas engine with exhaust gas recirculation (EGR) and a three-way catalyst 

(TWC) was developed. In addition, a Sturman camless Hydraulic Valve Actuation (HVA) 

system was used to improve efficiency. 

A Volvo 11 liter diesel engine was converted to operate as a stoichiometric natural gas engine. 

Operating a natural gas engine with stoichiometric combustion allows for the effective use of a 

TWC, which can simultaneously oxidize hydrocarbons and carbon monoxide and reduce NOx. 

High conversion efficiencies are possible through proper control of air-fuel ratio. Adding EGR 

lowers combustion chamber temperatures, which can improve efficiency, reduce the tendency to 

knock and lower engine out NOx emissions. 

A camless HVA system by Sturman Industries was applied to the engine. Using the HVA 

system can reduce pumping losses at light loads through either an early intake valve closing or a 

late intake valve closing (Miller cycle). The HVA system can also enable the use of high 

compression ratio pistons, where a lower effective compression ratio can be used at the high 

loads through either an early or a late intake valve closing, and higher compression ratios can be 

used at light to medium loads. Pistons with a 14.3:1 compression ratio were used on this engine. 

Emission tests were run at the 13-mode steady state test points and at three additional points 

(15% load at the low, intermediate, and high engine speeds). The results show a weighted 13-

mode NOx emission level of 0.005 g/kW-hr, which easily meets the emissions target of 0.27 

g/kW-hr (0.2 g/bhp-hr). Due to time and budget constraints, particulate matter was not 

measured, but is expected to be below the target of 0.013 g/kW-hr (0.01 g/bhp-hr). 

The high compression ratio pistons and variable valve timing available from the HVA system 

improved efficiency by 6.1% over a fixed valve timing cam based system using the weighted 13-

mode results. Further efficiency improvements may be possible through reduced losses of the 

HVA system and through improvement in light load combustion by using the HVA system to 

increase in-cylinder motion (swirl). 

1
1.0 INTRODUCTION 

Natural gas (NG) is an abundant energy source in this country that can be used as an automotive 

fuel. With rising fuel prices, many companies are seeking alternatives to imported oil to help 

contain fuel cost increases. However, only a small portion of current vehicles are powered by 

natural gas and gas vehicles are mainly operated by local and state municipalities. The National 

Renewable Energy Laboratory (NREL), led by the Center for Transportation Technologies and 

Systems, has the goal to help industry introduce alternative fueled vehicles into the marketplace 

by working with public and private organizations to develop and demonstrate innovative 

technologies to help reduce the nation’s dependence on imported oil. California has perhaps the 

most aggressive programs to help reduce pollution and curb the use of imported oil. Stringent 

fleet rules in California require that whenever public fleet operators with 15 or more vehicles 

replace or purchase new, the vehicle must use alternative fuels. NREL is leading the effort to 

develop the next generation heavy-duty natural gas engine to help reduce emissions in 

nonattainment areas. 

Emissions standards are also becoming increasingly stringent across the United States. 

Regulations for 2007 require that emissions be reduced from the current 2.5g/bhp-hr of 

NOx+NMHC to a phase-in level of 1.18 g/bhp-hr of NOx with NMHC less than 0.14 g/bhp-hr 

and particulate matter (PM) less than 0.01 g/bhp-hr. Meeting the PM standard with diesel 

engines will require the use of a diesel particulate filter (DPF). Heavy exhaust gas recirculation 

(EGR) will be required for NOx control. The NOx standard for 2010 is 0.2 g/bhp-hr for all 

heavy-duty engines. For the diesel engine to meet that standard, new NOx aftertreatment 

technology will be required. Natural gas engines have an advantage over diesel in that they 

operate on a gaseous fuel and are typically spark-ignited which emits lower PM by nature. This 

allows the combustion system to operate at or near stoichiometric air to fuel ratios (AFR), and 

maintain high tailpipe exhaust temperatures over the typical duty cycle when compared to a 

diesel engine. This allows a three-way catalyst (TWC) to be coupled to the exhaust system to 

oxidize CO and hydrocarbon (HC) emissions and reduce NOx. 

TWC technology was developed in the 1970’s for the automobile industry to clean up the 

emissions from the gasoline engine and also proved to be the most cost effective solution. Since 

then, TWC technology has evolved and demonstrated extremely low CO, HC, and NOx

emissions for the auto industry, which allows even lower emitting vehicles to be manufactured. 

Operating a heavy-duty natural gas (NG) engine with a TWC does not require special hardware. 

Proven control systems and sensors used for the light-duty industry can be applied to the heavyduty NG engine. EGR however, will need to be added for knock and exhaust temperature 

control as stoichiometric operation inherently increases the tendency for knock and engine out 

exhaust temperatures. Applying TWC technology to a heavy-duty NG engine leverages 35 + 

years of development as applied to light-duty gasoline engines and is a very cost effective 

solution for meeting future emissions standards. Mack Trucks Inc. is the leader in heavy-duty 

NG engines for use in the refuse industry. Waste Management (WM) is the leader in natural gas 

refuse haulers and operates a fleet of 400+ natural gas refuse haulers in southern California. 

2
NREL is funding a program with Volvo Powertrain (formerly Mack Powertrain) to demonstrate 

a next generation, stoichiometric natural gas engine with a TWC and a camless Hydraulic 

Actuated Valve (HVA) system. The engine is based on the Volvo MD11 diesel engine with 

natural gas components from the MG9 engine currently in production. 

1.1 Project Objective 

The objective of this project is to develop a low emissions natural gas engine. The emission 

targets for this project are 0.27 g/kW-hr (0.2 g/bhp-hr) of NOx and 0.013 g/kW-hr (0.01 g/bhphr) of particulate matter. To meet the objective, a chemically correct (stoichiometric) 

combustion, natural gas engine with exhaust gas recirculation (EGR) and a three-way catalyst 

(TWC) was developed. 

In addition to low emissions, diesel-like efficiencies are targeted through use of a Sturman 

camless Hydraulic Actuated Valve (HVA) system. The HVA system can reduce pumping losses 

at light loads through either an early intake valve closing or a late intake valve closing (Miller 

cycle). The HVA system can also enable the use of high compression ratio pistons. The 

compression ratio of a gas engine is limited by knock at high loads. With the HVA system, a 

lower effective compression ratio can be used at the high loads through either an early intake 

valve closing or a late intake valve closing, and higher compression ratios can be used at light to 

medium loads. 

3
2.0 TECHNICAL DISCUSSIONS/RESULTS 

A Volvo MD11 diesel engine (known as the MP7 engine in North America) was modified for 

operation on natural gas. Although there is not a gas version of the MD11 engine, there is a 

production gas version of the MD9 diesel engine known as the MG9 engine offered in Europe 

for Volvo Bus Corp., which is a stoichiometric, external high pressure EGR engine. Since the 

MD9 and MD11 engines share the same engine block and head, the conversion of the MD11 

engine to gas used many of the parts from the MG9 engine in addition to parts from the Mack 

E7G engine. The gas version of the MD11 engine will be designated as the MG11 engine. In 

addition to converting the engine to operate on gas, the Sturman HVA system was developed as 

well. Since this MG11 engine is the only Volvo 11 liter engine converted to operate on natural 

gas, baseline tests with a normal cam were not possible; therefore tests were conducted using the 

HVA system to simulate a fixed valve timing of a diesel cam with a typical compression ratio 

used for gas engines to obtain a baseline. Tests with throttleless operation and high compression 

ratio pistons were conducted using the HVA variable valve timing system and the results were 

compared to the baseline results. All efficiency comparisons (% increase) are in relative 

improvements, and not in efficiency points. 

2.1 Engine Description 

The engine arrived at SwRI as a natural gas engine with a high pressure EGR loop, a variable 

geometry turbocharger, and 10.25:1 compression ratio pistons with a Sturman HVA system 

partially installed. Components were added and or modified to convert the engine to a low 

pressure EGR loop with exhaust and intake breathing modified to minimize cylinder to cylinder 

distribution problems. The turbocharger was changed for a better match for this engine, high 

compression ratio pistons (14.3:1) were installed, and the Sturman HVA system installation was 

completed. 

Engine specifications are: 

• Volvo MG11 - 11 liter (659 cu. in.) displacement, 6-cyl inline, 4 valves per cylinder

• Bore x Stroke = 123 cm x 152 cm

• 325 bhp@1950 rpm

• Peak torque: 1180 lb-ft@1250 rpm

• Wastegated turbocharger with after cooler

• Low pressure, cooled EGR

• Compression Ratio = 14.3:1 (Baseline Compression ratio = 10.25:1)

• Spark plugs-- 6 – Denso 

• Ignition System – Volvo/Bosch Smart Coil on Plug

Fuel system specifications are: 

• Woodward Flotec “drive by wire” throttle control. Min Max automotive type 

• Servojet (SP021) natural gas injectors, 8 available, 6 used 

• Mack developed air / natural gas mixing ring and elbow 

4
• Stoichiometric, Closed – Loop 

• Fuel = LNG, CNG 

• Fuel pressure set point = 100-120 psi 

2.1.1 Engine Breathing 

The engine breathing includes the intake system, the exhaust system, the turbocharger and the 

EGR loop. The engine arrived at SwRI with an end fill intake manifold, a variable geometry 

turbocharger, and a high pressure V-Pulse EGR loop. The engine was modified as described 

below. 

2.1.1.1 Intake Manifold 

The end fill intake manifold was replaced with a center fill manifold. The center fill provides a 

more even cylinder-to-cylinder distribution of the fuel and air mixture. A picture of the end fill 

intake manifold is shown in Figure 1. A picture of the center fill intake manifold is shown is 

Figure 2. The center fill manifold was mounted upside down so that the throttle and mixing 

elbow would not interfere with the HVA transfer plate. 

Figure 1. End Fill Intake Manifold 

5
Figure 2. Center Fill Intake Manifold 

2.1.1.2 Exhaust System and Turbocharger 

The turbocharger on the engine was a variable geometry turbocharger. Since a low pressure 

EGR loop was used, a VGT was not needed to drive EGR, and it was decided to use a fixed 

geometry turbocharger with a wastegate. The wastegate on the turbocharger only bypassed 

exhaust gases on one side of the divided housing; therefore an external wastegate was used. A 

wastegate system was setup to bypass exhaust gases from both sides of the divided exhaust 

manifold. A picture of the external wastegate is shown on Figure 3. 

6
Figure 3. External Wastegate 

2.1.1.3 EGR System 

The EGR system was changed from a high pressure loop to a low pressure loop, where the EGR 

is routed from the exhaust system after the turbine, though a laboratory heat exchanger, to an 

EGR valve, and into the intake system before the compressor on the turbocharger. A picture of 

the EGR system is shown in Figure 4. The fan in the picture was used to cool the wastegate. 

7
Figure 4. Low Pressure EGR Loop 

2.1.2 Engine Ignition System 

The engine ignition system is adapted from the MG9 ignition system. The coil extensioner and 

coil tube have been elongated to fit with the special valve space made for the HVA system. 

8
Ignition Coil

Coil Sleeve

Coil Extension

Spark Plug 

Tube

Spark Plug

Valve Cover

Valve Cover 

Spacer

Cylinder 

Head

Figure 5. Engine Ignition System 

2.1.3 Engine Pistons 

Aluminum pistons are chosen to avoid high surface temperature and they are also easy to 

machine. Fourteen (14) low compression ratio (10.25:1) pistons are made for baseline testing. 

Compared to the MD11 pistons, MG11 pistons have the cooling gallery removed in order to have 

enough space for reduced compression ratio. The compression height was reduced to 

accommodate the higher thermal deformation on the crown. The piston ring groves were 

redesigned as well. 

Seven (7) high compression ratio (14.3:1) pistons are designed to better utilize the variable valve 

timing capability. 

Seven (7) blank pistons are reserved for unexpected situations during engine testing. 

9
Figure 6. Piston Designs, Left – 10.25:1 CR, Right – 14.3:1 CR 

2.1.4 Engine Control System 

For this natural gas engine, a Rapid Prototyping Electronic Control System (RPECS) was used. 

The RPECS is a PC based control system that uses C++ as the programming language, which 

provided full user flexibility for electronic controls. The RPECS allows for “on the fly” changes 

in the engine calibration. Typical algorithms for a natural gas engine were used. 

2.1.5 HVA System 

The major parts of the Hydraulic Valve Actuation (HVA) system are the pump cart, the Valve 

Drive Module (VDM), the desktop computer, the transfer plate to mount the actuators and oil 

rails to the head, the oil rails, and the actuators. The possible variable valve motion includes: 

• Exhaust Valve Opening 

• Exhaust Valve Lift 

• Exhaust Valve Closing Landing Rate 

• Exhaust Valve Closing 

• Intake Valve Ramp Hold Duration 

• Intake Valve Opening 

• Intake Valve Lift 

• Intake Valve Closing Landing Rate 

• Intake Valve Closing 

A picture of the HVA oil rails and actuatorsis shown in Figure 7. Figure 8 shows the VDM and 

Figure 9 shows the hydraulic pump cart. Further information of the Sturman HVA system can 

be obtained from Sturman. 

10
Figure 7. Sturman HVA System 

Figure 8. Sturman Valve Drive Module (VDM) 

11
Figure 9. Hydraulic Pump Cart for the HVA System 

2.2 Engine Development 

Engine development was conducted in a steady-state test cell. 

2.2.1 Test Cell Description 

The steady-state test cell uses an eddy current dynamometer to absorb power. A heat exchanger 

is used for the engine coolant where the engine out coolant temperature is controlled to a 

specified temperature. A heat exchanger is also used for the intercooler, where the intercooler 

out temperature is controlled to a specified temperature. Natural gas was used for the testing, 

where it is compressed into a storage tank, and then delivered to the test cell where regulators 

reduce the pressure to a specified level (~110-120 psi). A gas chromatograph records the gas 

composition on an hourly basis. The average gas composition during the engine testing is shown 

in Table 1 along with the standard deviation. 

12
TABLE 1. AVERAGE GAS COMPOSITION AND STANDARD DEVIATION FOR 

DEVELOPMENT WORK 

Component Concentration (vol %) Standard Deviation 

Methane 94.22 0.40 

Ethylene 0.00 0.00 

Ethane 2.82 0.34 

Propane 0.54 0.12 

Butanes 0.21 0.06 

C5+ 0.12 0.03 

Carbon Dioxide 1.06 0.13 

Nitrogen 1.02 0.16 

Hydrogen Sulfide 0.00 0.00 

Data were recorded with the SwRI data acquisition system. The data recorded are shown in 

Table 2. All equipment was calibrated according to SwRI Standard Operating Procedure for 

Calibration and Maintenance. The efficiency recorded by the SwRI data acquisition system does 

not include the power required to drive the hydraulic pump for the Sturman HVA system. 

TABLE 2: DATA RECORDED 

Misc Run Number 

Date 

Time 

# of Points Averaged 

Engine Speed 

Torque 

Fuel Flow 

Air Flow 

Relative Humidity 

Calculated BTE 

BSFC 

BSEC 

BMEP 

Power 

Air Fuel Ratio 

Equivalence Ratio 

Fuel H/C Ratio 

Fuel O/C Ratio 

Fuel N/C Ratio 

Stoich Air Fuel Ratio 

Fuel Molecular Weight 

Fuel High Heating Value 

Fuel Low heating Value 

Reactive H/C Ratio 

Specific Humidity 

EGR Rate 

Pressure Fuel 

Barometric 

Inlet Restriction 

Boost Before Intercooler 

Boost After Intercooler 

Intake Manifold 

Pre-Turbine 

Exhaust Restriction 

Oil Gallery 

Temperature Coolant In 

Coolant out 

Fuel 

Ambient Air 

Boost Before Intercooler 

Boost After Intercooler 

Compressor Inlet 

Intake Manifold 

Exhaust Stack 

Individual Exhaust (6) 

Pre-Turbine 

Oil Gallery 

Oil Sump 

Catalyst (3) 

13
Fuel 

Composition 

Nitrogen 

Methane 

Carbon Dioxide 

Ethane 

Hydrogen Sulfide 

Propane 

Iso-Butane 

Butane 

Iso-Pentane 

Pentane 

Hexanes 

Heptanes 

Octanes 

Iso-Nonanes 

Ethylene 

Emissions 

Emissions 

Calculations 

CO 

HC 

NOx 

CO2 

O2 

Intake CO2 (for EGR) 

BSCO 

BSHC 

BSNOx 

Corrected BSNOx 

Equivalence Ratio 

EGR Rate 

2.2.2 Engine Calibrations 

A typical calibration for a natural gas engine was used. EGR rates were selected based on 

previous engine data on a Mack E7GT engine. Ignition timing was set to maintain ~15° ATDC 

location of peak pressure. Equivalence ratios were set to provide low NOx and CO emissions 

after the catalyst. Typically, just slightly rich of stoichiometric provides the lowest emissions for 

natural gas engines. 

 

2.2.3 Test Points 

Steady state testing was conducted. The plan was to perform a 22-mode test. The 22-mode test 

is a combination of the 13-mode steady state test, also known as the European Stationary Cycle 

(ESC) or Organisation Internationale des Constructeur D’Automobiles (OICA) test, and the 

SwRI 16-mode test. The 13-mode test is used in certification of the engine. The 16-mode test 

was developed to cover some of the areas that the 13-mode does not, such as light loads (<25% 

load) and/or low engine speeds (< peak torque speed). These are typically the areas where the 

calibration could be significantly different from higher speed and load points. The test points are 

shown in Table 3 and Figure 10. Speed values have been rounded to a convenient test point. The 

speeds for the 16-mode and 22-mode test points are based on a more typical low speed at idle 

(600 rpm) and a more typical high speed at rated power (1950 rpm). The 13-mode speeds are 

based on the requirements of the Code of Federal Regulations (CFR), where the low speed is 

defined as the lowest engine speed where 50% of the maximum power occurs and the high speed 

is defined as the highest engine speed where 70% of the maximum power occurs. The 25% 

speed, as defined for the 13-mode, is typically the same as the more typical 50% speed or peak 

torque speed of the engine. The 75% speed, as defined for the 13-mode, is typically the same as 

the more typical 100% speed or peak power speed of the engine. Due to time and budget 

constraints, the testing was reduced to mode 1 and modes 8-22. These points are shown in 

Figure 11. 

14
TABLE 3: STEADY STATE TEST POINTS 

22 

Mode 

Speed 

** Load Speed 

(rpm) 

Torque 

(N-m) 

16 

Mode 

13 

Mode 

13 

Mode 

Weight 

Speed for 

the 13 

Mode *** 

1* 0% 0% 600 160 1 1 15% idle 

2 15% 15% 800 146 2 

3 15% 50% 800 488 3 

4 15% 100% 800 976 4 

5 30% 15% 1000 203 5 

6 30% 50% 1000 678 6 

7 30% 100% 1000 1356 7 

8* 50% 15% 1250 240 8 

9* 50% 25% 1250 400 7 5% 25% 

10* 50% 50% 1250 800 9 5 5% 25% 

11* 50% 75% 1250 1200 6 5% 25% 

12* 50% 100% 1250 1600 10 2 8% 25% 

13* 75% 15% 1600 206 11 

14* 75% 25% 1600 344 9 10% 50% 

15* 75% 50% 1600 688 12 3 10% 50% 

16* 75% 75% 1600 1032 4 10% 50% 

17* 75% 100% 1600 1376 13 8 9% 50% 

18* 100% 15% 1950 178 14 

19* 100% 25% 1950 297 11 5% 75% 

20* 100% 50% 1950 593 15 13 5% 75% 

21* 100% 75% 1950 890 12 5% 75% 

22* 100% 100% 1950 1186 16 10 8% 75% 

* Tested 

** With idle as the low speed and rated power as the high speed 

*** With the low and high speeds as defined by the 40CFR86 

15
0

200

400

600

800

1000

1200

1400

1600

1800

0 500 1000 1500 2000 2500

Engine Speed (rpm)

Torque (N-m)

Peak Torque Rated Power

Figure 10. 22-Mode Steady State Test Points 

0

200

400

600

800

1000

1200

1400

1600

1800

0 500 1000 1500 2000 2500

Engine Speed (rpm)

Torque (N-m)

Peak Torque Rated Power

Figure 11. 16 Steady State Modes Tested 

2.2.4 Problems 

During the course of the program, there were some problems that occurred. These include a 

broken valve, foreign material entering the engine through the intake system, excessive valve 

wear, and noise on the HVA system. 

16
The first problem that occurred was a broken valve. The head on an intake valve on the number 

3 cylinder fractured and embedded itself into the top of the piston. A picture of the cylinder head 

with the missing valve head is shown in Figure 12. The valve head embedded in piston is shown 

in Figure 13. It is assumed that the valve had contact with the piston multiple times and failed 

due to bending fatigue. All of the valves that were hitting the piston showed some bending. A 

picture of the result from a piston versus valve collision is shown in Figure 14. The software for 

the HVA system was updated to disable the valve when a valve to piston collision is detected 

through the valve position feedback signal. This problem occurred with the 10.25:1 compression 

ratio piston, which were then replaced with the 14.3:1 compression ratio pistons. The original 

valves and valve seats in the head were from the MG9 engine. The valve seats were ground and 

the valves were replaced with MD11 valves. 

Figure 12. Broken Intake Valve Head on Cylinder 3 

17
Figure 13. Valve Head Embedded in the Piston 

18
Figure 14. Marks on the Piston from Valve/Piston Collisions 

The second problem that occurred during testing was foreign material entering the engine and 

embedding itself on the number one piston. A picture of the foreign material is shown in Figure 

15. The foreign material appeared to be valve material from the previous valve failure. It is 

assumed that the material had lodged itself somewhere in the engine before the rebuild, and 

dislodged when running the engine after the rebuild. The number one piston was replaced and 

the intake valves and valve seats on the number one cylinder were reground. 

19
Figure 15. Foreign Material on the Number One Piston 

The third problem that occurred was excessive valve wear. Figure 16 shows one of the valves, 

but all of the valves showed excessive wear after approximately 50 hours of testing. The head 

was rebuilt with new MD11 valve seat inserts and valves. The MG9 valve seats, which were 

originally in the head, induce more swirl than the MD11 valve seats. The excessive wear was a 

result of material incompatibility, where the diesel MD11 valves were used with the natural gas 

MG9 valve seats. The head was rebuilt with new MD11 valve seat inserts and valves. Changing 

the valve seats from the original MG9 design to the MD11 design cause a reduction in the in 

cylinder swirl. Only the preliminary data was run with the MG9 seats. 

20
Figure 16. Excessive Valve Wear 

The fourth problem was noisy signals on the HVA system. Both the command signals for the 

actuators and the feedback signals were noisy. A picture from an oscilloscope of the feedback 

signal on one of the valves is shown in Figure 17. This data were recorded in a simulation mode 

(engine not actually running, but the HVA system detects that it is running). This figure shows 

that the early intake valve opening was caused by a noisy command signal. The HVA system 

was also detecting valve to piston collisions when the intake valve ramp and hold function was 

turned on. The clearance between the valve and piston is small when the piston is at top dead 

center (TDC) and the intake valve opened. If the noise on the feedback system is larger than the 

clearance, the Sturman system will detect a collision and disable the valve. This problem was 

solved by insulating the metal connectors under the valve cover for both the command signals 

and feedback signals. 

21
Figure 17. Oscilloscope Picture Showing an Early Intake Valve Opening Command 

2.3 Valve Timing Sweeps 

With the Sturman HVA system, the time needed for testing with all the possible valve timing 

configurations (as described in section 2.1.3) is much greater than the time allowed for this 

project. Therefore reduced testing as described in the following sections was conducted. 

2.3.1 Preliminary Valve Timing Sweeps 

Preliminary valve timing sweeps were conducted on the engine after the HVA system 

installation was completed but before all of the other modifications were performed. The engine 

had a low pressure EGR loop, the center fill manifold, and the 10.25:1 compression ratio pistons. 

The purpose of these preliminary timing sweeps was to show the efficiency improvements of late 

and early intake valve closing at light loads. A late or early intake valve closing at light loads 

reduces the effective compression ratio but also reduces pumping losses. Figure 18 shows a 

4.7% improvement in efficiency for a late intake valve closing and a 6.2% improvement for an 

early intake valve closing. The exhaust valve opening, exhaust valve closing, and intake valve 

opening were set to simulate a normal cam. Both intake and exhaust valve lifts were set to 10 

mm and the intake ramp and hold was turned off. 

22
1250 rpm, 25% Load, 5% EGR

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 50 100 150 200 250 300

Intake Valve Duration (CAD)

Efficiency Gain (%)

0

20

40

60

80

100

Throttle (%)

Figure 18. Preliminary Testing for Late and Early IVC 

2.3.2 Valve Timing Sweeps 

Valve timing sweeps were conducted on the HVA variable timing engine as shown below. 

• Vary exhaust valve opening 

3⁄4 Exhaust valve closing set to simulate a normal cam 

3⁄4 Intake valve opening set to simulate a normal cam 

3⁄4 Intake valve closing used to set torque though an early closing at light loads or set to 

simulate a normal cam at medium to high loads with early intake valve closing used 

to lower the effective compression ratio at the highest loads where knock is 

encountered 

3⁄4 Intake and exhaust valve lifts set for 10 mm, unless reduced exhaust valve lift was 

needed to lower exhaust temperatures 

3⁄4 Intake ramp and hold set for the minimum duration, unless it was turned off to lower 

exhaust temperatures 

• Vary Exhaust Valve Closing 

3⁄4 Exhaust valve opening set for maximum efficiency based on above results 

3⁄4 Intake valve opening set to simulate a normal cam 

3⁄4 Intake valve closing used to set torque though an early closing at light loads or set to 

simulate a normal cam at medium to high loads with early intake valve closing used 

to lower the effective compression ratio at the highest loads where knock is 

encountered 

3⁄4 Intake and exhaust valve lifts set for 10 mm, unless reduced exhaust valve lift was 

needed to lower exhaust temperatures 

3⁄4 Intake ramp and hold set for the minimum duration, unless it was turned off to lower 

exhaust temperatures 

23
• Vary Intake Valve Opening 

3⁄4 Exhaust valve opening set for maximum efficiency based on above results 

3⁄4 Exhaust valve closing set for maximum efficiency based on above results 

3⁄4 Intake valve closing used to set torque though an early closing at light loads or set to 

simulate a normal cam at medium to high loads with early intake valve closing used 

to lower the effective compression ratio at the highest loads where knock is 

encountered 

3⁄4 Intake and exhaust valve lifts set for 10 mm, unless reduced exhaust valve lift was 

needed to lower exhaust temperatures 

3⁄4 Intake ramp and hold set for the minimum duration, unless it was turned off to lower 

exhaust temperatures 

2.3.2.1 Full Timing Sweeps 

Testing began with Mode 15 of the 22 modes, which is 1600 rpm, 50% load (700 N-m). Results 

are shown in Figures 19-21. All of these test points are at a 100% throttle with load controlled 

by an early intake valve closing. Figure 19 shows the effect of varying the exhaust valve 

opening. Efficiency peaks at an opening of 164° for 5% EGR, 152° for 10% EGR, and 168° for 

15% EGR. Figure 20 shows the effect of varying the exhaust valve closing using the peak 

efficiency point for exhaust valve opening. The trend for exhaust valve closing is increasing 

efficiency with a later closing. The latest exhaust valve closing is limited by the piston to valve 

clearance. Figure 21 shows the effect of varying the intake valve opening using the peak 

efficiency point for exhaust valve opening and closing. Efficiency peaks at an opening of 374° 

for both 5% and 10% EGR and 390° for 15% EGR. For all of these curves, efficiency 

differences are small. 

30

31

32

33

34

35

120 130 140 150 160 170 180 190 200

Exhaust Valve Opening (deg)

BTE (%)

5% EGR 10% EGR 15% EGR

EGR - 5%

EVO - Vary

EVC - 338 deg

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 10%

EVO - Vary

EVC - 338 deg

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 15%

EVO - Vary

EVC - 351 deg

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

Figure 19. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load 

Varying Exhaust Valve Opening 

24
30

31

32

33

34

35

320 325 330 335 340 345 350 355 360 365

Exhaust Valve Closing (deg)

BTE (%)

5%EGR 10% EGR 15% EGR

EGR - 5%

EVO - 164 deg

EVC - Vary

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 10%

EVO - 152 deg

EVC - Vary

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 15%

EVO - 164 deg

EVC - Vary

IVO - 377 deg

IVC - EIVC to maintain load

IVO Ramp - 40 deg

Figure 20. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load 

Varying Exhaust Valve Closing 

30

31

32

33

34

35

365 370 375 380 385 390 395 400 405

Intake Valve Opening (deg)

BTE (%)

5% EGR 10% EGR 15% EGR

EGR - 5%

EVO - 164 deg

EVC - 351 deg

IVO - Vary

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 10%

EVO - 152 deg

EVC - 351deg

IVO - Vary

IVC - EIVC to maintain load

IVO Ramp - 40 deg

EGR - 15%

EVO - 152 deg

EVC - 351 deg

IVO - Vary

IVC - EIVC to maintain load

IVO Ramp - 40 deg

Figure 21. Mode 15 of the 22 Mode Test, 1600 rpm, 50% Load 

Varying Intake Valve Opening 

Full timing sweeps continued with modes 9, 19, 11, 14, and 10. Similar efficiency trends were 

observed for these modes, the results of all the full timing sweeps are presented in Appendix A. 

The full timing sweep tests indicate that: 

25
• Exhaust valve opening has little effect on efficiency within the range of openings tested. 

Further changes in exhaust valve opening, beyond the range tested, are expected to 

reduce efficiency 

 

• Exhaust valve closing should be as late as possible for highest efficiency 

• Intake valve opening should be close to as early as possible for highest efficiency 

The speeds and loads for these modes are shown in Figure 22. 

0

200

400

600

800

1000

1200

1400

1600

1800

0 500 1000 1500 2000 2500

Engine Speed (rpm)

Torque (N-m)

Peak Torque Rated Power

25% Load

50% Load

75% Load

Figure 22. Full Timing Sweeps Test Points 

2.3.2.2 Reduced Timing Sweeps 

Based on the information from the full timing sweeps, it was decided to shorten the testing at 

each mode to three exhaust valve opening timings, three exhaust valve closing timings, and three 

intake valve opening timings at a single EGR rate. The valve timings are shown in Table 4, and 

the EGR rates will be determined by previous testing on the Mack E7GT engine (NREL Report 

No. SR-540-38222). The latest possible exhaust valve closing and earliest possible intake valve 

opening are limited by piston to valve clearance. 

TABLE 4. REDUCED VALVE TIMING MATRIX 

EVO EVC IVO 

160 degrees The latest possible setting +4 degrees from the earliest 

possible setting 

164 degrees -4 degrees from the latest 

possible setting 

+8 degrees from the earliest 

possible setting 

168 degrees -8 degrees from the latest 

possible setting 

+12 degrees from the earliest 

possible setting 

26
Results at Mode 16, which is 1600 rpm, 75% load (1032 N-m), are shown in Figures 23-25 for 

varying exhaust valve opening (EVO), exhaust valve closing (EVC) and intake valve opening 

(IVC) respectively. The throttle was set to 100%, the intake valve closing set to 536°, and the 

wastegate was used to set the load. 

31

32

33

34

35

36

120 130 140 150 160 170 180 190 200

Exhaust Valve Opening (deg)

BTE (%)

EGR - 15%

EVO - Vary

EVC - 351 deg

IVO - 374 deg

IVC - 536 deg

IVO Ramp - 36 deg

Figure 23. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load 

Varying Exhaust Valve Opening 

31

32

33

34

35

36

340 345 350 355 360 365

Exhaust Valve Closing (deg)

BTE (%)

EGR - 15%

EVO - 164 deg

EVC - Vary

IVO - 374 deg

IVC - 536 deg

IVO Ramp - 36 deg

Figure 24. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load 

Varying Exhaust Valve Closing 

27
31

32

33

34

35

36

370 375 380 385 390 395 400 405

Intake Valve Opening (deg)

BTE (%)

EGR - 15%

EVO - 164 deg

EVC - 351 deg

IVO - Vary

IVC - 536 deg

IVO Ramp - 36 deg

Figure 25. Mode 16 of the 22 Mode Test, 1600 rpm, 75% Load 

Varying Intake Valve Opening 

Reduced timing sweeps continued with modes 16, 8, 13, 18, 12, 20, and 21. Similar 

efficiency trends were observed for these modes, the results of all the reduced timing sweeps are 

presented in Appendix B. Single test points were recorded for modes 22, 17, and 1. Modes 22 

and 17 are 100% load at 1950 and 1600 rpm respectively. At these test points, there was no 

knock margin, and only one test point was recorded. Mode 1 is idle, and only one test point was 

recorded due to time and budget constraints. Results for the single point tests are included in 

Appendix C. 

2.3.3 Final Calibration 

Based on the above results, emissions tests at each of the modes were conducted at the highest 

efficiency point for each mode. The emissions and efficiency results for each mode are shown in 

Table 6. The composite (weighted) emissions for the 13-mode are 0.005 g/kw-hr of NOx, 1.166 

g/kW-hr of CO, and 0.536 g/kW-hr of THC. 

28
TABLE 6. EFFICIENCY AND EMISSIONS RESULTS 

Mode * Speed Load Speed 

(rpm) 

Torque 

(N-m) 

MG11 

BTE 

(%) 

NOx After 

Cat 

(g/kW-hr) 

CO After 

Cat 

(g/kW-hr) 

THC After 

Cat 

(g/kW-hr) 

1 (1) 0% 0% 600 160 17.5 0.015 1.337 10.165 

8 50% 15% 1250 240 24.1 0.087 0.555 0.116 

9 (7) 50% 25% 1250 400 28.6 0.001 0.664 0.095 

10 (5) 50% 50% 1250 800 33.4 0.002 0.055 0.060 

11 (6) 50% 75% 1250 1200 36.3 0.005 1.621 0.299 

12 (2) 50% 100% 1250 1600 37.9 0.006 1.707 0.427 

13 75% 15% 1600 206 20.9 0.003 1.570 0.000 

14 (9) 75% 25% 1600 344 26.3 0.003 0.785 0.019 

15 (3) 75% 50% 1600 688 32.9 0.006 1.967 0.317 

16 (4) 75% 75% 1600 1032 35.3 0.003 0.166 0.125 

17 (8) 75% 100% 1600 1376 37.6 0.004 1.754 0.775 

18 100% 15% 1950 178 17.9 0.003 1.214 0.037 

19 (11) 100% 25% 1950 297 23.6 0.000 1.549 0.108 

20 (13) 100% 50% 1950 593 30.7 0.007 1.175 0.874 

21 (12) 100% 75% 1950 890 34.4 0.008 0.957 0.485 

22 (10) 100% 100% 1950 1186 35.3 0.007 0.819 0.572 

Weighted 13-Mode 33.9 0.005 1.166 0.536 

* Number in parentheses is the corresponding mode for the 13-mode test

The operational settings for the above data are shown in Table 7. 

TABLE 7. OPERATIONAL SETTINGS 

Mode EVO 

(°) 

EVC 

(°) 

IVO 

(°) 

IVC 

(°) 

Ramp 

(°) 

EGR 

(%) 

Spark 

Timing 

(°btdc) 

In Lift 

(mm) 

Ex Lift 

(mm) 

1 164 344 380 429 0 0 9 10 8 

8 164 345 376 444 28 5 22 10 10 

9 162 343 376 465 28 5 20 10 10 

10 164 349 376 536 28 10 19 10 10 

11 160 349 378 536 28 10 19 10 10 

12 164 345 376 489 28 10 21 10 10 

13 160 351 374 450 36 5 24 7 10 

14 164 343 382 467 36 5 20 10 10 

15 164 351 377 509 36 5 21 10 10 

16 164 351 378 536 36 15 26 10 10 

17 168 351 374 480 0 12.5 28 9 10 

18 152 348 373 456.5 44 5 25 7 10 

19 152 351 373 481 44 10 26 6 10 

20 160 351 373 499 0 10 25 10 7 

21 160 351 373 485 0 12.5 30 7 7 

22 168 351 373 475 0 14 32 7 9 

29
The emissions results before the catalyst for each mode are shown in Table 8. The composite 

(weighted) emissions for the 13-mode are 6.896 g/kw-hr of NOx, 13.178 g/kW-hr of CO, and 

6.933 g/kW-hr of THC. The conversion efficiencies of the TWC are over 99% for NOx, 91% for 

CO, and 92% for THC. 

TABLE 8. BEFORE CATALYST EMISSIONS RESULTS 

Mode * Speed Load Speed 

(rpm) 

Torque 

(N-m) 

NOx

Before 

Cat 

(g/kW-hr) 

CO Before 

Cat 

(g/kW-hr) 

THC 

Before Cat 

(g/kW-hr) 

1 (1) 0% 0% 600 160 4.308 142.094 31.517 

8 50% 15% 1250 240 6.548 11.416 4.936 

9 (7) 50% 25% 1250 400 10.377 13.984 6.628 

10 (5) 50% 50% 1250 800 5.811 11.290 7.372 

11 (6) 50% 75% 1250 1200 5.689 14.709 7.897 

12 (2) 50% 100% 1250 1600 9.053 12.530 5.995 

13 75% 15% 1600 206 5.693 16.911 9.987 

14 (9) 75% 25% 1600 344 6.991 11.292 5.479 

15 (3) 75% 50% 1600 688 5.046 18.099 9.849 

16 (4) 75% 75% 1600 1032 5.586 11.648 6.154 

17 (8) 75% 100% 1600 1376 2.827 19.112 12.202 

18 100% 15% 1950 178 6.861 12.359 7.299 

19 (11) 100% 25% 1950 297 8.621 13.464 7.690 

20 (13) 100% 50% 1950 593 4.308 142.094 31.517 

21 (12) 100% 75% 1950 890 6.548 11.416 4.936 

22 (10) 100% 100% 1950 1186 10.377 13.984 6.628 

Weighted 13-Mode 6.764 14.213 7.024 

* Number in parenthesis is the corresponding mode for the 13-mode test 

The emissions target for NOx for this engine has been achieved, but efficiencies do not show an 

improvement over the Mack E7GT stoichiometric EGR engine (efficiency comparisons are 

presented in the following sections). Particulate matter was not measured due to time and budget 

constraints, but is expected to be below the target. The efficiencies for the Volvo 11 liter HVA 

engine should show a higher efficiency than an engine with a cam due to both a higher 

compression ratio and reduced pumping losses (throttleless operation, particularly at light loads). 

In addition, the efficiency comparison shown in Table 6 does not include valve train losses 

(power needed to run the hydraulic pump) for the Volvo 11 liter HVA engine. These efficiency 

results are not higher than a typical natural gas engine such as the Mack E7GT. The major 

reason for the difference in efficiencies is that the E7GT is a mature engine whereas the Volvo 

11 liter is a new gas engine which has not been optimized. 

2.4 Baseline Testing 

To evaluate the efficiency improvement an HVA system can provide, baseline tests were 

conducted on the MG11 engine. The 14.3:1 compression ratio pistons were replaced with the 

30
original 10.25:1 pistons, which is the same compression ratio used on the MG9 engine. Tests at 

the 16 modes were conducted with valve timings set to approximate a cam. The throttle was 

used to control torque where the wastegate was fully open at light loads and was used to control 

manifold air pressure at higher loads. The valve timings and efficiencies for the baseline tests 

are shown in Table 9. 

TABLE 9. BASELINE TEST CONDITIONS 

Mode Speed 

(rpm) 

Load 

(%) 

EVO 

(deg) 

EVC 

(deg) 

IVO 

(deg) 

IVC 

(deg) 

Ramp 

(deg) 

Int 

Valve 

Lift 

(mm) 

Exh 

Valve 

Lift 

(mm) 

BTE 

(%) 

1 600 0% 168 347 379 536 0 10 10 17.7 

8 1250 15% 164 349 376 545 28 10 10 20.8 

9 1250 25% 164 349 376 545 28 10 10 25.5 

10 1250 50% 164 349 376 545 28 10 10 31.5 

11 1250 75% 164 349 376 545 0 8 8 34.1 

12 1250 100% 164 349 376 545 0 5/10 10 35.7 

13 1600 15% 162 350 374.5 550 36 10 10 19.2 

14 1600 25% 162 350 374.5 550 36 10 10 24.3 

15 1600 50% 162 350 374.5 550 0 5/10 10 29.9 

16 1600 75% 162 350 374.5 550 0 5/10 10 32.2 

17 1600 100% 162 350 374.5 550 0 5/10 10 33.6 

18 1950 15% 160 351 373 555 44 10 10 16.7 

19 1950 25% 160 351 373 555 0 5/10 10 21.3 

20 1950 50% 160 351 373 555 0 5/10 10 27.7 

21 1950 75% 160 351 373 555 0 5/10 10 30.3 

22 1950 100% 160 351 373 555 0 5/10 10 33.4 

2.5 Results Analysis 

The efficiency improvements of an HVA system on a natural gas engine are discussed below. 

2.5.1 Baseline Efficiency 

The baseline testing on the MG11 engine was conducted with the HVA valve timing set to 

simulate a normal cam and without HVA hydraulics pumping losses included in the efficiency 

calculation. To obtain a more accurate baseline, simulations were conducted on this engine to 

obtain the difference between the valve profile of using the HVA system to simulate a cam and 

the actual valve lift profile with a cam. Figure 26 shows the valve lift difference between the 

HVA system and a cam. 

31
0 100 200 300 400 500 600 700 800

Crank Angle (deg)

Valve Lift

HVA Exhaust HVA Intake

Cam Exhaust Cam Intake

Figure 26. Valve Lift Profile for the HVA system and a Cam 

 

The simulation provides a relative performance difference between the HVA system and a cam, 

therefore the relative change in efficiency from the simulations were applied to the test data. The 

efficiency data represents a normal cam, but still does not include the cam losses. Cam losses 

were applied to the data to arrive at a baseline efficiency which represents an engine with a cam. 

The results are shown in Table 10. The last column represents the baseline case. Idle was not 

modeled therefore a relative efficiency change was not applied at idle. 

TABLE 10. BASELINE EFFICIENCY RESULTS 

Mode Speed 

(rpm) 

Load 

(%) 

BTE from Test 

Data, HVA 

Fixed Timing 

(%) 

BTE from 

HVA Sim 

(%) 

BTE from 

Cam Sim 

(%) 

BTE 

w/ cam 

w/o cam losses 

(%) 

BTE 

w/cam 

& cam losses 

(%) 

1 600 0% 17.7 - - 17.7 17.0 

8 1250 15% 20.8 23.0 23.3 21.0 20.5 

9 1250 25% 25.5 26.9 27.0 25.6 25.2 

10 1250 50% 31.5 33.6 34.1 31.9 31.6 

11 1250 75% 34.1 35.3 35.5 34.2 34.1 

12 1250 100% 35.7 38.8 39.2 36.0 35.9 

13 1600 15% 19.2 20.9 21.9 20.1 19.4 

14 1600 25% 24.3 24.8 25.2 24.7 24.2 

15 1600 50% 29.9 31.8 31.3 29.4 29.1 

16 1600 75% 32.2 33.6 34.7 33.3 33.1 

17 1600 100% 33.6 34.5 35.2 34.2 34.1 

18 1950 15% 16.7 17.8 18.0 16.9 16.3 

19 1950 25% 21.3 21.7 21.7 21.3 20.9 

20 1950 50% 27.7 28.3 28.5 27.9 27.5 

21 1950 75% 30.3 31.6 32.0 30.7 30.5 

22 1950 100% 33.4 31.6 32.3 34.1 33.9 

Weighted 13-Mode 31.1 31.3 

32
2.5.2 HVA Efficiency 

The HVA testing on the MG11 engine was conducted without HVA hydraulics pumping losses 

included in the efficiency calculation. Pumping requirements were obtained on this system (a 

research type system) and applied to the data. Table 11 shows the HVA efficiency results. The 

last column represents an HVA system with hydraulic pumping losses included. 

TABLE 11. HVA EFFICIENCY RESULTS 

Mode Speed 

(rpm) 

Load 

(%) 

BTE from 

Test Data, 

HVA 

Variable 

Timing (%) 

BTE 

w/Pumping 

losses 

(%) 

1 600 0% 17.5 13.3 

8 1250 15% 24.1 20.4 

9 1250 25% 28.6 26.0 

10 1250 50% 33.4 31.8 

11 1250 75% 36.3 35.2 

12 1250 100% 37.9 37.0 

13 1600 15% 20.9 17.4 

14 1600 25% 26.3 23.6 

15 1600 50% 32.9 31.2 

16 1600 75% 35.3 34.1 

17 1600 100% 37.6 36.6 

18 1950 15% 17.9 14.3 

19 1950 25% 23.6 20.8 

20 1950 50% 30.7 28.8 

21 1950 75% 34.0 33.0 

22 1950 100% 35.3 34.2 

Weighted 13-Mode 33.9 32.4 

2.5.3 Optimized Natural gas Efficiency 

The efficiency data from the Mack E7GT data was used as an optimized natural gas engine. The 

E7GT engine has an 11.5:1 compression ratio, whereas efficiency improvements with the HVA 

system will be compared to a baseline engine with a 10.25:1 compression. The E7GT efficiency 

data was modified to reflect the efficiency at a compression ratio of 10.25:1, so that the 

efficiency improvement is applied to an engine with the same compression ratio as the baseline. 

The theoretical efficiency is given by the following equation: 

)1(

1 1 − −= γ η CR

Where: 

 CR = compression ratio 

γ = ratio of specific heats = 1.4 

33
For a 10.25:1 compression ratio, the theoretical efficiency is 60.6%, and for an 11.5:1 

compression ratio, the theoretical efficiency is 62.4%. The efficiency of the 10.25:1 

compression ratio is 97% of the efficiency of the 11.5:1 compression ratio. Although the actual 

efficiency numbers are unrealistic, the relative change in efficiency is realistic. Therefore the 

efficiency of the E7GT engine was reduced by 3% to arrive at the 10.25:1 compression ratio 

E7GT efficiency. The efficiencies are shown in Table 12. 

TABLE 12. E7GT EFFICIENCY RESULTS 

Mode Speed 

(rpm) 

Load 

(%) 

E7GT 11.5 

CR BTE (%) 

E7GT 10.25 

CR BTE (%) 

1 600 0% 21.3 20.7 

8 1250 15% 25.2 24.5 

9 1250 25% 30.6 29.7 

10 1250 50% 35.9 34.9 

11 1250 75% 38.4 37.3 

12 1250 100% 39.1 38.0 

13 1600 15% 21.8 21.2 

14 1600 25% 28.2 27.4 

15 1600 50% 33.8 32.9 

16 1600 75% 36.8 35.8 

17 1600 100% 37.9 36.8 

18 1950 15% 18.8 18.2 

19 1950 25% 24.5 23.8 

20 1950 50% 31.8 30.9 

21 1950 75% 35.5 34.5 

22 1950 100% 36.6 35.5 

Weighted 13-Mode 35.1 34.1 

2.5.4 Diesel Efficiency 

Efficiency data for a 2010 diesel engine (same emissions level target as the MG11 HVA engine) 

are not currently available, but data for engines certified US EPA 2004 standards are. 

The data for the heavy-duty engines are an average of four engines ranging from 12.0 to 15.2 

liters (average of 14.0 liters). The data for the medium-duty engines are an average of three 

engines ranging from 5.9 to 8.8 liters (average of 6.9 liters). Since the 11 liter MG11 engine falls 

in between the medium and heavy duty engine size, the average of the two was used for the 

diesel comparison to the MG11 HVA engine. In addition, it is expected that efficiencies will be 

reduced by 2% for 2007, and will not change for 2010 (efficiency for 2010 includes both fuel 

costs and cost of operating an aftertreatment device). 

Table 13 shows the 2004 and expected 2010 diesel efficiencies. Only data at the ESC 13-mode 

test points are available. 

34
TABLE 13. DIESEL EFFICIENCY 

Mode Speed 

(rpm) 

Load 

(%) 

2004 Diesel 

BTE (%) 

2010 Diesel 

Estimated 

BTE (%) 

1 600 0% 5.6 5.4 

8 1250 15% 

9 1250 25% 35.7 35.0 

10 1250 50% 38.2 37.4 

11 1250 75% 39.7 38.9 

12 1250 100% 40.7 39.9 

13 1600 15% 

14 1600 25% 33.2 32.5 

15 1600 50% 37.5 36.7 

16 1600 75% 39.2 38.4 

17 1600 100% 40.2 39.4 

18 1950 15% 

19 1950 25% 29.6 29.0 

20 1950 50% 34.7 34.0 

21 1950 75% 37.1 36.4 

22 1950 100% 38.0 37.3 

Weighted 13-Mode 37.9 37.1 

2.5.5 Efficiency Comparison 

A comparison of the efficiencies is shown in Table 14 and a bar chart of the weighted 13-mode 

results is shown in Figure 27. Each of the efficiency columns in Table 14 is described below. 

1. This column is the estimated efficiency of the MG11 engine with a cam and 10.25:1 

compression ratio pistons. It is estimated from actual data on the MG11 HVA engine 

using valve timings that simulate a fixed cam (hydraulic pumping losses are not included 

in this data). The efficiencies were then modified based on simulations of this engine 

with HVA valve timing and normal cam valve timing to get a efficiencies of an MG11 

with a cam (but still without valve train losses). Finally, valvetrain losses of the cam 

system were applied to arrive at the MG11 Cam Baseline BTE. 

2. This column shows the efficiency of the MG11 engine with the HVA system using valve 

timings that simulate a fixed cam and 10.25:1 compression ratio pistons. It is estimated 

from actual data on the MG11 HVA engine using valve timings that simulate a fixed cam 

(hydraulic pumping losses are not included in this data) and then an estimate of hydraulic 

pumping losses of the research oriented system were applied to arrive at the MG11 HVA 

Fixed Timing BTE. 

3. This column shows the efficiency of the MG11 engine with the HVA system using 

variable valve timings and 14.3:1 compression ratio pistons. It is estimated from actual 

data on the MG11 HVA engine using variable valve timings (hydraulic pumping losses 

35
are not included in this data). Hydraulic pumping losses of the research oriented system 

were applied to arrive at the MG11 HVA Variable Timing BTE. 

4. This column shows the efficiency from the E7GT engine with 11.5:1 compression ratio 

pistons. This efficiency is from actual data. 

5. This column shows the estimated efficiency of the E7GT engine at a compression ratio of 

10.25:1. It is estimated from the actual data with the efficiency reduction of changing the 

compression ratio from 11.5:1 to 10.25:1 CR to arrive at the E7GT 10.25:1 CR BTE. 

6. This column shows the estimated efficiency of the E7GT engine if it had the HVA 

system with valve timing set to simulate a normal cam. It is estimated by applying the 

same change in efficiency of the MG11 engine from the HVA fixed timing (with 

pumping losses) to the cam baseline (with valvetrain losses) to arrive at the E7GT 10.25 

CR HVA Fixed Timing BTE. 

7. The column shows the estimated efficiency of the E7GT engine with a 14.3:1 

compression ratio and a variable timing HVA system. It is estimated by applying the 

change in efficiency from the MG11 cam baseline (including valvetrain losses) to the 

MG11 HVA variable timing engine (with pumping losses of a research oriented system) 

to the E7GT engine at a compression ratio of 10.25:1 to arrive at the BTE Improvement 

Applied to the E7GT. The research system has full capabilities for valve control full, 

which requires a certain amount of power to properly operate the system 

8. The column shows the estimated efficiency of the E7GT engine with a 14.3:1 

compression ratio and a variable timing HVA system with a production oriented system. 

It is estimated by applying the change in efficiency from the MG11 cam baseline 

(including valvetrain losses) to the MG11 HVA variable timing engine (with pumping 

losses of a production oriented system) to the E7GT engine at a compression ratio of 

10.25:1 to arrive at the BTE Improvement Applied to the E7GT. The production system 

assumes that the full power of a research system will not be necessary for proper 

operation, and reduced pumping losses can be realized with a system that only includes 

the required valve control for a production system. 

9. This column shows the estimated efficiency of a 2010 diesel engine. It is based on data 

for engines certified to 3.35 g/kW-hr (2.5 g/bhp-hr) of NOx+NMHC. The efficiencies 

were reduced by 2% (relative change) to represent the loss in efficiency and/or increase 

operating cost to arrive at the 2010 Diesel BTE. 

36
TABLE 14. EFFICIENCY COMPARISON 

9 

2010 

Diesel 

BTE Est 

(%) 

5.4 

- 

35.0 37.4 38.9 39.9 

- 

32.5 36.7 38.4 39.4 

- 

29.0 34.0 36.4 37.3 37.1 

8 

Product 

Oriented 

HVA 

BTE 

Increase 

Applied 

to E7GT 

(%) 

20.7 26.9 32.4 36.1 39.3 39.8 20.8 28.1 36.3 37.6 40.1 17.8 25.2 33.3 38.2 36.4 36.2 

7 

Research 

Oriented 

HVA 

BTE 

Increase 

Applied 

to E7GT 

(%) 

16.2 24.5 30.8 35.2 38.7 39.3 18.9 26.6 35.4 37.0 39.6 16.0 23.8 32.4 37.5 35.9 35.4 

6 

E7GT 

10.25 CR 

HVA 

Fixed 

Timing 

BTE (%) 

16.5 21.2 27.5 33.2 36.3 37.0 17.3 24.7 32.1 33.7 35.4 15.1 21.5 29.2 33.1 34.0 32.3 

5 

E7GT 

10.25 CR 

BTE (%) 

20.7 24.5 29.7 34.9 37.3 38.0 21.2 27.4 32.9 35.8 36.8 18.2 23.8 30.9 34.5 35.5 34.1 

4 

E7GT 

11.5 CR 

BTE (%) 

21.3 25.2 30.6 35.9 38.4 39.1 21.8 28.2 33.8 36.8 37.9 18.8 24.5 31.8 35.5 36.6 35.1 

3 

MG11 

Research 

Oriented 

HVA 

Variable 

Timing 

BTE (%) 

13.3 20.4 26.0 31.8 35.2 37.0 17.4 23.6 31.2 34.1 36.6 14.3 20.8 28.8 33.0 34.2 32.4 

2 

MG11 

HVA 

Fixed 

Timing 

BTE (%) 

13.5 17.7 23.2 30.0 33.1 34.9 15.9 21.8 28.3 31.1 32.7 13.5 18.8 26.0 29.1 32.4 29.8 

1 

MG11 

Cam 

Baseline 

BTE (%) 

17.0 20.4 25.1 31.5 34.0 35.8 19.4 24.2 29.0 33.0 34.0 16.3 20.8 27.5 30.4 33.8 31.2 

Load 

0% 

15% 25% 50% 75% 

100% 

15% 25% 50% 75% 

100% 

15% 25% 50% 75% 

100% 

Speed 

0% 

50% 50% 50% 50% 50% 75% 75% 75% 75% 75% 

100% 100% 100% 100% 100% 

Mode 

1 8 9 

10 11 12 13 14 15 16 17 18 19 20 21 22 

Weighted 13-mode 

37
28

29

30

31

32

33

34

35

36

37

38

MG11 Cam

Baseline BTE

(%)

MG11 HVA

Fixed Timing

BTE (%)

MG11

Research

Oriented

HVA

Variable

Timing BTE

(%)

E7GT 11.5

CR BTE (%)

E7GT 10.25

CR BTE (%)

E7GT 10.25

CR HVA

Fixed Timing

BTE (%)

Research

Oriented

HVA BTE

Improvement

Applied to

E7GT (%)

Production

Oriented

HVA BTE

Improvement

Applied to

E7GT (%)

2010 Diesel

BTE Est (%)

Figure 27. 13-Mode Weighted Efficiencies 

Adding valvetrain losses to the MG11 baseline cam engine reduces the efficiency by 1.0% 

(relative efficiency) on the weighted 13-mode results, whereas adding pumping losses of a 

research system to the MG11 HVA variable timing engine reduces efficiency by 4.3%, but 

adding pumping losses of a production system to the MG11 HVA variable timing engine reduces 

efficiency by 2.2%. 

Figure 28-30 shows the efficiencies at 1250, 1600, and 1950 rpm respectively. Figure 31 shows 

the efficiency change of an engine with a HVA system compared to an engine with a cam. The 

highest efficiency improvements are at higher loads, whereas there is an efficiency loss at the 

lower loads. Part of this is due to the increase in losses associated with operating an HVA 

system, where the losses are more significant with the HVA system at the lighter loads. Part of 

this may be the loss of turbulence with the 100% throttle position used with the HVA system. At 

light loads, the turbulence created by the throttle assists in the combustion process. Further 

testing with the HVA system should be conducted with one intake valve open more than the 

other to create turbulence at light loads. Figure 32 shows the efficiency changes of a HVA 

system compared to a 2010 diesel engine. At the high loads, the efficiencies approach the diesel 

efficiency, but are still lower at the lighter loads. The research oriented pumping losses for the 

HVA system were based on engine speed only. A production system that can reduce pumping 

losses could improve efficiencies. 

38
20

25

30

35

40

45

0% 20% 40% 60% 80% 100%

Load

BTE (%)

MG11 Variable Timing

MG11 Cam Baseline

E7GT Baseline

E7GT Improved

2007/2010 Diesel

Figure 28. Efficiencies at 1250 rpm 

20

25

30

35

40

45

0% 20% 40% 60% 80% 100%

Load

BTE (%)

MG11 Variable Timing

MG11 Cam Baseline

E7GT Baseline

E7GT Improved

2007/2010 Diesel

Figure 29. Efficiencies at 1600 rpm 

39
20

25

30

35

40

45

0% 20% 40% 60% 80% 100%

Load

BTE (%)

MG11 Variable Timing

MG11 Cam Baseline

E7GT Baseline

E7GT Improved

2007/2010 Diesel

Figure 30. Efficiencies at 1950 rpm 

-15%

-10%

-5%

0%

5%

10%

0% 20% 40% 60% 80% 100%

Load

Efficiency Improvement

1250 rpm

1600 rpm

1950 rpm

Figure 31. HVA System Efficiency Improvement over a Cam System 

40
-20%

-15%

-10%

-5%

0%

5%

10%

0% 20% 40% 60% 80% 100%

Load

Efficiency Improvement

1250 rpm

1600 rpm

1950 rpm

Figure 32. HVA System Efficiency Improvement over a 2010 Diesel Engine 

41
3. SUMMARY AND CONCLUSIONS 

The summary and conclusions of the project are: 

• A Volvo 11 liter diesel engine was converted to natural gas with a camless hydraulic 

valve actuation system. 

3⁄4 A Sturman HVA system was installed on the engine. 

3⁄4 The engine had not been optimized for operation on natural gas. 

• Tests were conducted with high compression ratio pistons using an early intake valve 

closing to either operate throttleless at light loads or reduce the effective compression 

ratio at high loads. 

3⁄4 The Sturman system enables throttleless operation, using early intake valve closing to 

control load. 

3⁄4 The Sturman HVA system enables full use of high compression ratio pistons, where 

full compression ratio can be used at light loads and a reduced effective compression 

ratio can be used at high loads to avoid knock. 

• The engine efficiency is not sensitive to intake opening, exhaust opening, or exhaust 

closings within a fairly large range of valve timings. 

• The HVA system can improve the efficiency of a heavy duty gas engine. 

3⁄4 With pumping losses of a research system included, efficiency improvements of an 

HVA system over a cam system are realized down to 25% load, at 15% load, there is 

an efficiency penalty due to high hydraulic pumping losses of the HVA system and 

lack of turbulence from throttleless operation. 

3⁄4 More intelligent control of hydraulic pumping requirements for the HVA system at 

light loads could improve efficiency. 

3⁄4 Turbulence can be created with a throttleless engine through different valve lifts on 

the two intake valves. 

• When comparing a natural gas engine with a research HVA system to a 2010 diesel 

engine, efficiencies at the higher loads are equivalent, but efficiencies at the lower loads 

are still higher with the diesel engine. 

3⁄4 A research HVA system has 4.7% lower relative efficiency on the weighted 13-mode 

than an equivalent diesel engine, but a production HVA system has 2.5% lower 

relative efficiency. 

• Low emissions are possible with stoichiometric combustion, EGR and a TWC. 

3⁄4 The NOx emissions on the 13-mode test are 0.005 g/kW-hr, which are well below the 

target of 0.27 g/kW-hr. 

3⁄4 Particulate matter was not measured, but is expected to be below the target of 0.013 

g/kW-hr. 

42
F1146-E(12/2004) 

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

October 2006 

2. REPORT TYPE

Subcontract Report 

3. DATES COVERED (From - To)

12/16/03 - 7/31/06 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

US10 Capable Prototype Volvo MG11 Natural Gas Engine 

Development: Final Report, December 16, 2003 – July 31, 2006 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-540-40756 

5e. TASK NUMBER

WO14.1000 

6. AUTHOR(S)

C. Tai, T. Reppert, J. Chiu, L. Christensen, K. Knoll, and J. Stewart 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Mack Trucks, Inc. 

Volvo Powertrain North America 

13302 Pennsylvania Avenue 

Hagerstown, Maryland 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ZCI-4-32050-01 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

NREL/SR-540-40756 

12. DISTRIBUTION AVAILABILITY STATEMENT

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U.S. Department of Commerce 

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13. SUPPLEMENTARY NOTES

NREL Technical Monitor: Aaron Williams 

14. ABSTRACT (Maximum 200 Words)

The report discusses a project to develop a low-emissions natural gas engine with exhaust gas recirculation (EGR) 

and a three-way catalyst (TWC) 

15. SUBJECT TERMS

natural gas engines; vehicle emissions; exhaust emissions; exhaust gas recirculation; EGR; three-way catalyst; TWC

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