ICCT study compares leading global driving cycles and provides usable conversion factors for CO2 emissions

8 December 2014

A team at the International Council on Clean Transportation (ICCT) has compared the dynamics of the four leading driving cycles worldwide—the US CAFE standards (a composite of FTP75 and HWFET); the New European Driving Cycle (NEDC); Japan’s JC08; and the recently developed Worldwide Harmonized Light-Duty Test Cycle (WLTC)—and their impacts on fuel consumption and CO₂ emissions on an equal basis. (WLTC will be replacing NEDC in a few years.)

The result is a set of usable conversion factors for distance-based CO₂ emissions among the different driving cycles. The ICCT team determined these factors on distinct levels of detail, characterized by technology parameters such as share of diesel engines in the fleet, vehicle size, share of hybrid systems, aerodynamic drag, and others. This study updates and refines an earlier analysis completed in 2007. (Earlier post.) The new study uses a different methodology with different mathematical approaches.

<!——>

For the study, the ICCT team simulated CO₂ and efficiency results over the test cycles for a variety of vehicle and technology packages using a vehicle emission model developed by Ricardo Engineering. Model runs based on the speed courses of the driving cycles were resolved on a second-by-second basis. The researchers focused on current vehicle architectures and advanced innovative technologies in 2020/2025 timeframe.

The direct comparison of CO₂ or FC standards’ stringencies from different regions not only depends on the different driving cycles applied but also on the technical characteristics of the regional vehicle fleets. The use of comprehensive adjustment factors therefore requires simplifying assumptions concerning the assessment of averaged fleet compositions.

Cycle deviations of CO₂ emissions averaged over all gasoline and diesel technologies resulting from basic single regression approach with zero intercept. The error bars here represent the standard deviations caused by individual vehicle technology packages. Gasoline vehicles emit strongest under the WLTC schedule. CO₂ emissions under the JC08, US CAFE and NEDC regimes are 18%, 15% and 13% lower.

The cycle-specific deviations of diesel vehicles are generally lower and show a different pattern. For example, averaged WLTC and JC08 emissions (the highest deviations for the gasoline vehicles) are almost equal for diesel, while CAFE emissions are lower than JC08 (the opposite of the gasoline vehicles). These results reflect the fundamental differences in the structures of gasoline and diesel engine maps. Source: ICCT. Click to enlarge.

Ricardo developed a complete, physics-based vehicle and drivetrain system model and implemented it in MSC.Easy5, a commercially available software package for vehicle system analysis that models the physics in the vehicle drivetrain during a drive cycle. Torque reactions are simulated from the engine through the transmission and driveline to the wheels. The model reacts to simulated driver inputs to the accelerator and brake pedals, thus enabling the actual vehicle acceleration to be determined based on a realistic control strategy.

The model determines key component outputs such as torque, engine speeds, and heat rejection. The combination of these engine load output data with fuel or CO₂ engine maps results in integral emission data for specific driving cycles.

Ricardo parameterized the CO₂ model for the predefined driving cycles and vehicle technologies and developed a user-friendly application tool, Data Visualization Tool (DVT) or Complex System Tool.

ICCT also commissioned Ricardo to assess likely technology developments occurring until 2020/2025, taking into account six different LDV classes: B, C, D, small CUV, small and large N1.

CO₂ savings was evaluated separately for gasoline and diesel concepts. The most promising technologies in terms of both reduction potential and market penetration in 2020/2025 were identified and explored further. The most relevant developments related to:

• improvements in transmissions and clutches (automatic, dual clutch transmission [DCT] continuously variable transmission [CVT]);
• advanced engines (valve controls, lean combustion, exhaust gas recirculation [EGR], direct injection, Atkinson);
• system electrification (parallel and powersplit hybrids); and
• efficient operation strategies such as stop/start systems.

The ICCT team applied different types of regression analyses to the modeled emission data to describe the dependencies for each pair of the different driving cycles. The regression types differ by the mathematical nature (linear vs. nonlinear approaches), the inclusion or exclusion of the y-intercept, the differentiation into different vehicle technologies and the inclusion of additional independent variables (multiple regression analyses). Therefore, the level of complexity and the achievable quality of the regression results vary among the different types, the ICCT authors noted.

They developed a general pattern to assist users in determining which conversion approach is most appropriate in each case and which regression coefficients should
be applied.

Resources

• Jörg Kühlwein, John German, and Anup Bandivadekar (2014) “Development of test cycle conversion factors among worldwide light-duty vehicle CO₂ emission standards”

Tenneco introduces new large engine SCR system for marine applications; NOx reduction 90%; production targeted 2015

8 December 2014

Tenneco has introduced a complete urea dosing control, fluid handling and catalyst solution for selective catalytic reduction (SCR) aftertreatment, enabling large engines to meet EPA Tier IV and IMO Tier III regulations. Tenneco’s new marine SCR system has demonstrated effective NO_x reduction in bench and field testing. In laboratory validation, the system achieved average NO_x reduction efficiency levels of more than 90%.

<!——>

The system is designed specifically for high-horsepower engines in the marine, stationary and locomotive markets, providing precise and reliable delivery of liquid urea. It includes a proprietary, high-performance injector design, a precision mechatronic fluid delivery pump and customizable remote monitoring and controls.

Tenneco’s large engine SCR system is designed to meet the requirements of major maritime classification societies including the ABS (American Bureau of Shipping), DNV (Det Norske Veritas), CCS (China Classification Society), KR (Korean Register of Shipping) and Class NK (Nippon Kaiji Kyokai). The system is currently being validated with marine and large engine customers, and is expected to be ready for production in 2015.

The fluid delivery system with dosing control software is capable of managing multiple injection points and sensors. The system can support urea flows up to 120 meters, which enables a wide array of installation options. Airless urea injection provides high dosing accuracy and consistency.

The system’s unique Human Machine Interface (HMI) can be accessed on the front of the fluid delivery box or remotely via a touch screen tablet. It features an easy-to-use interface to access onboard diagnostic functions and to monitor and control all system parameters, including but not limited to NO_x reduction performance and urea concentration levels in real time.

In addition to effective emissions reduction, field testing highlighted how the system’s form, fit, function and performance capabilities can be easily integrated into a vessel’s engine and control architecture. Field tests were conducted on a 224 ft. Great Lakes training vessel powered by four 800 horsepower, circa 1984 Tier 0 engines. In a series of validation tests, including the ISO 8178 E2 cycle, when outfitted with the aftertreatment system, the 1984 Tier 0 engines met all criteria for IMO Tier III and EPA Tier III compliance including NO_x, HC and SO_x.

Tenneco has also tested the same SCR aftertreatment technology in a stationary diesel generator set, demonstrating the system’s flexibility and scalability across multiple applications. When installed on a 970 horsepower, Tier II engine running ISO 8178 D2 cycle, the engine met all criteria for marine EPA Tier IV compliance.

Penn State researchers develop thermally regenerative ammonia battery (TRAB) for efficient waste heat recovery

8 December 2014

Researchers at Penn State University have demonstrated the efficient conversion of low-grade thermal energy into electrical power using a thermally regenerative ammonia-based battery (TRAB). A paper on their work is published in the RSC journal Energy Environmental Science.

The battery uses copper-based redox couples [Cu(NH₃)₄²⁺/Cu and Cu(II)/Cu]. Ammonia addition to the anolyte (the electrolyte surrounding the anode) of a single TRAB cell produced a maximum power density of 115 ± 1 W m⁻² (based on projected area of a single copper mesh electrode), with an energy density of 453 Wh m⁻³ (normalized to the total electrolyte volume, under maximum power production conditions).

<!——>

Adding a second cell doubled both the voltage and maximum power. Increasing the anolyte ammonia concentration from 2M to 3 M further improved the maximum power density to 136 ± 3 W m⁻².

The battery will run until the reaction uses up the ammonia needed for complex formation in the electrolyte near the anode or depletes the copper ions in the electrolyte near the cathode. Then the reaction stops.

To “recharge”, the TRAB uses low-grade waste heat from an outside source. The researchers distill ammonia from the effluent left in the battery anolyte and then recharge it into the original cathode chamber of the battery. The chamber with the ammonia now becomes the anode chamber and copper is re-deposited on the electrode in the other chamber, now the cathode, but formerly the anode. The researchers switch ammonia back and forth between the two chambers, maintaining the amount of copper on the electrodes.

The concept of the TRAB. Zhang et al. Click to enlarge.

Volatilization of ammonia from the spent anolyte by heating (simulating distillation), and re-addition of this ammonia to the spent catholyte chamber with subsequent operation of this chamber as the anode (to regenerate copper on the other electrode), produced a maximum power density of 60 ± 3 W m⁻², with an average discharge energy efficiency of ~29% (electrical energy captured versus chemical energy in the starting solutions).

Power was restored to 126 ± 5 W m⁻² through acid addition to the regenerated catholyte to decrease pH and dissolve Cu(OH)₂ precipitates, suggesting that an inexpensive acid or a waste acid could be used to improve performance.

The researchers note that the current thermally regenerative ammonia battery is not optimized, so that further work could both produce more power and reduce the cost of operating the batteries.

These results demonstrated that TRABs using ammonia-based electrolytes and inexpensive copper electrodes can provide a practical method for efficient conversion of low-grade thermal energy into electricity.

Other researchers on this project were Jia Liu, postdoctoral fellow and Wulin Yang, graduate student, both in environmental engineering. The researchers have filed a preliminary patent on this work.

The King Abdullah University of Science and Technology supported this work.

Resources

• Fang Zhang, Jia Liu, Wulin Yang and Bruce E. Logan (2015) “A thermally regenerative ammonia-based battery for efficient harvesting of low-grade thermal energy as electrical power,” Energy Environ. Sci. doi: 10.1039/C4EE02824D

Mitsubishi Electric verifies VP-X high-efficiency turbine generator; first 900-MVA-class generator with indirect H2 cooling; 99% efficiency

8 December 2014

Mitsubishi Electric Corporation has successfully completed verification tests on its VP-X turbine generator for thermal power plants—the first generator in the 900-MVA class to use indirect hydrogen cooling for stator conductors. (Hydrogen is used extensively in power generation to cool turbine generators because of its low density and good thermal characteristics.)

<!——>

Cooling is achieved with hydrogen gas introduced from outside of the main insulation. Due to this and other proprietary technologies, the VP-X achieves an extra-high efficiency rating of 99%, placing it in the world’s highest class of turbine generators that offer highly sustainable operation. A series of VP-X generators will be launched commercially in April 2015.

Lineup of two-pole turbine generators. Source: Mitsubishi Electric. Click to enlarge.

Mitsubishi Electric enhanced cooling performance in the VP-X by improving main insulation and cooling gas ventilation without incorporating a water-cooling system for the stator winding. Until now, all large-capacity turbine generators in the 900 MVA class have relied on water-cooling.

Mitsubishi Electric’s VP-X features a simplified design that will help improve the appearance of power plants, as well as lower the requirements for maintaining and operating turbine generators. The overall size is 20% smaller than conventional indirectly hydrogen-cooled generators. In addition, both the footprint and frame diameter are smaller, making transportation easier.

Elimination of a water-cooling system for the stator winding helps to simplify maintenance. Also, needs for manual inspection have been reduced through a partial discharge monitoring system that incorporates a microstrip antenna for continuous monitoring of the main insulation and an inspection robot.

In addition, a new parallel-manufacturing method for the stator core and stator frame shortens delivery time.

The VP-X turbine generator received a 2014 Good Design Award from the Japan Institute of Design Promotion, making this the first large electrical machine for power systems to be so honored.

Mitsubishi Electric has shipped more than 2,000 turbine generators worldwide since 1908.

UW Madison team investigates cycle-to-cycle combustion instability in HCCI and RCCI

8 December 2014

Researchers at the University of Wisconsin-Madison have used computational fluid dynamics modeling to investigate cycle-to-cycle instability of homogeneous charge compression ignition (HCCI) and reactivity-controlled compression ignition (RCCI) engines—two approaches to low-temperature combustion. Low-temperature combustion engines offer the promise of simultaneously increasing engine efficiency and reduce NO_x and PM emissions, but have not been widely implemented due to difficulties controlling combustion phasing, combustion duration, and cycle-to-cycle variation.

<!——>

A paper on their study is published in the International Journal of Engine Research.

They performed a large design of experiment with small perturbations to the intake and fueling conditions, then fit a response surface model to the design of experiment results to predict the combustion characteristics and to determine the main sources of cycle-to-cycle variation.

Results showed that:

• Reactivity-controlled compression ignition and homogeneous charge compression ignition have significantly more variation than conventional diesel combustion.

• Reactivity-controlled compression ignition combustion phasing (CA50—crank angle when 50% of fuel is burned) is most sensitive to variations in diesel fuel mass, level of exhaust gas recirculation, and charge gas temperature. The peak pressure rise rate of reactivity-controlled compression ignition combustion is most sensitive to variations in gasoline fuel mass.

• Sources of variation for homogeneous charge compression ignition are similar to those of reactivity-controlled compression ignition combustion; however, trapped gas pressure and cylinder liner temperature become significant factors.

• Because of the late combustion phasing required for homogeneous charge compression ignition to maintain acceptable pressure rise rate, its cycle-to-cycle variation was found to be higher than that of reactivity-controlled compression ignition combustion for the same input variations.

Resources

• David Klos, Sage L Kokjohn (2014) “Investigation of the sources of combustion instability in low-temperature combustion engines using response surface models,”
  International Journal of Engine Research doi: 10.1177/1468087414556135