Technology Development Analysis on Low Carbon for Power of Heavy-Duty Commercial Vehicle
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Commercial vehicle industry worldwide is facing challenges from environmental pressures, stringent limits of CO2 emission, governmental regulations as well as ever-increased customer demands. This paper analyzes the above-mentioned challenges, especially in China, including the potential improvement to increase the brake thermal efficiency (BTE), with five levels of BTE proposed, ranging from current 45 to 60% in future, corresponding to China fuel consumption regulation (CFCR) in different phases. The authors also proposed the technology roadmaps to meet the upcoming CFCR3 and CFCR4; finally, the authors draw the conclusions to conform with ever-stringent regulation in China.
KeywordsHeavy-duty diesel engine (HDDE) Low carbon Fuel consumption
Environmental issues are attracting increasing attention worldwide, especially the problem of climate change associated with carbon emissions. International communities have reached the agreement to limit the global average temperature rise within 2 °C and accumulated carbon dioxide emission ever within 3.2 trillion tons in the future. In 2015, 195 countries signed the Paris Agreement, which came into effect in 2016 to limit the carbon emission. Chinese government committed to peak carbon emission in 2030, to reduce the carbon emission by 60–65% per unit GDP from the level of 2005.
2 Potential Improvements in HDDE BTE
Globally, OEMs are striving to obtain a BTE of 50% solely on the basis of improved engine designs, and BTE values of 55% are anticipated following the adoption of Rankine cycle technology.
3 Technology Roadmap for Low-Carbon HDDEs having a BTE of 50%
CFCR3 requires a 15% reduction in fuel consumption compared with CFCR2. The engine will contribute 35%, which needs fuel saving about 5% for engine. Currently HDDE BTE in general is 43–45%, and to meet CFCR3 and keep product competitive in market, BTE of 47% is a challenging target.
HDDE has the potential to meet BTE of 47% based solely on improvements to the engine, while maintaining a reasonable TCO. OEMs should consider that lean combustion design is the key to engine optimization, so as to avoid large investments associated with other structural redesigns. For future CFCR4, various innovative technologies intended to reduce fuel consumption by combustion optimization are presented herein, which may allow future vehicles to meet the requirements of CFCR4.
3.1 Optimization of the Combustion Process
There are three criteria involved in selecting new technologies for implementation: effectiveness, benefit and competitiveness. The latter can in turn be categorized into differentiation, innovation and charming characteristic. Reductions in losses due to friction and accessories or in threshold characteristics are necessary, so combustion optimization should contribute to more than 80% of the fuel saving to achieve the BTE target. Improvements in the fuel injection system, combustion chamber and turbocharging are also being considered by the China FAW.
There are four technologies available for optimization of combustion process, i.e., fuel injection and supply, combustion chamber shape optimization, optimization of initial flow in cylinder, charge quality and composition as well as compression and expansion .
Fuel injection and supply system have the potential to increase the BTE by 1.5%, which includes variable injection rates, rapid combustion and optimization of the injection timing and pressure. Combination of combustion chamber shape optimization and optimization of initial flow in cylinder may have 1.0% of BTE gain .
Asymmetrical supercharging plus electromechanical turbocharger will increase 1% of BTE in terms of charging.
The spatial and temporal zone control strategies were developed, and evaluation criteria were set up. Consequently, the air utilization rate and high-temperature region were optimized so as to ensure properly distributed combustion. The associated experimental results demonstrate that a 2–5 g/kWh reduction in the brake specific fuel consumption can be achieved, while maintaining the same NOx level.
3.2 Reduction in Losses
The potential approaches to reducing friction losses include antifriction coatings and low-viscosity oil. In addition, the energy consumption of various accessories, including the variable oil pump, clutch air compressor and electric thermostat, could all be lowered. The use of low-viscosity oil in conjunction with a variable rate oil pump is projected to increase the BTE by 0.5%.
4 The Correlation of Energy Consumption with Fuel Combustion
Fuel reduction from engine operation point of view is considered. Both hybrid electric vehicle (HEV) and intelligent and connected vehicle (ICV) technologies are important means of reducing fuel consumption, while nature gas engine will develop fast as it is one of the effective ways from alternative fuel point of view for CO2 emission reduction. In addition, waste heat recovery can greatly increase efficiency, depending on the vehicle operating conditions. Because various running modes require different system designs, OEMs must improve their system design capabilities in a cooperative manner with vehicle design.
With the C-WTVC, the CO2 emission from heavy commercial natural gas vehicles is 7.1% lower than those from diesel vehicles. As such, natural gas is the most suitable low-carbon fuel for heavy-duty commercial vehicles . With the tractor express conditions in China, the CO2 emissions from liquid natural gas (LNG) vehicles are also approximately 5.9% less than those generated by diesel vehicles. Thus, meeting the low-carbon and environmental protection requirements under the green development principle of the Chinese government may require the increased adoption of heavy commercial natural gas vehicles.
Reducing the fuel consumption for HEVs is greatly dependent on the operational mode because frequent start and stop modes have more potential for energy recovery. In the C-WTVC vehicle testing cycle, buses and delivery vehicles demonstrated greater potential for lower fuel usage, with savings of up to 7%. Based on balancing weight and efficiency, hybrid vehicles are evidently best suited to long haul transportation. Other future technology for reducing CO2 emissions in conjunction with ICV is predictive cruise control. However, the benefit of this technology depends on the grade value and frequency of the roads being travelled, with hilly terrain up and downhill resulting in a 3–5% fuel saving on average. Platooning based on technology of Cooperative Adaptive Cruise Control (CACC) could also drastically reduce air drag, thus lowering fuel usage by an additional 4–7%.
Upcoming CO2 emissions regulations in China represent a challenge that will greatly affect the development of commercial vehicle technologies and products. This legislation will have a significant impact on the automotive industry over the next decade. In addition to the CFCR3 and CFCR4 requirements, another key driver for CO2 emissions abatement will be competition to develop more fuel-efficient vehicles for both global and domestic markets.
Different technologies will be adopted to meet these challenges, depending on the market segment. China FAW considers that HDDE will realize maximum BTE, but those improvements in fuel and hybrid technologies will also be achieved. Other innovative technologies related to green vehicles are necessary, including intelligent, connected transportation, and will likely be adopted by the Chinese automobile industry to further reduce CO2 emissions.
Significant changes in customer demands, regulations and policies are anticipated over the next decade in China.
The most important driver for future vehicle design will be the fuel consumption, which is both a so-called threshold and excitement attribute, and a regulatory requirement.
China FAW developed BTE levels up to 60%, and with detailed potential analysis based on energy distribution from tank to wheel, FAW proposed that the greatest challenge lies in creating engine concept without adoption of Rankine cycle technology to meet BTE 50%.
China FAW developed FDCR technologies, including injection modes, combustion chamber redesign and E-ATW, to meet the BTE goal of 47%.
ICE and NEV powertrain platforms will be necessary to meet the new regulations. The following points should be considered.
Continued research and development of ICE and NEV powertrain platforms will be required.
Technology roadmaps for ICE powertrain add-on strategies have been developed, involving an NEV powertrain cut-down strategy.
The pace of new technology upgrades should be controlled based on just-in-time management principles.
Reducing costs while implementing upgrades to core technologies will necessitate the use of lean design.
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