JSAE Exposition 2015: Envisioning future of powertrains for passenger cars (1) (trends in Japan)

Japanese OEMs show direction of ICE development amidst growing environmental concerns



 The Automotive Engineering Exposition 2015 was held at the Pacifico Yokohama on May 20 to 22 by the Society of Automotive Engineers of Japan, Inc. (JSAE). During the 2015 JSAE Annual Congress (Spring) that was held as part of the Exposition, lectures were given on the theme of "Seeking the mainstream powertrain for passenger vehicles after 2025" by experts in automotive industry, government and academic institutions. Reported below are the lectures presented by engineers representing four carmakers.

 What prompted the auto industries is the need to find ways to fight the growing concern with CO2 emissions and ease the impacts of air pollution and global warming. All four carmakers seem to agree that electric vehicles (EVs) and plug-in hybrid vehicles (PHVs) may make their way but that does not mean the extinction of internal combustion engines (ICE). Therefore, reducing CO2 emissions from ICEs is a crucial technical issue that requires an on-going solution through the future. Introduced below are the directions of technical development of ICEs envisaged by four Japanese carmakers.

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Environmental and energy issues surrounding automobiles

Environmental and energy issues
Created by MarkLines based on materials from Honda R&D Co., Ltd.

 Air pollution caused by exhaust gases was once a social issue in cities. Today, warming of earth's atmosphere due to CO2 and other greenhouse gases has become a major issue requiring a global attention. Another impending issue is the introduction of renewable energies. These issues are expected to become more serious than they already are.



Regulations on fuel economy

Regulations on fuel economy in different countries
Created by MarkLines based on materials from Honda R&D Co., Ltd.

 To tackle the environmental energy issues, increasingly stringent regulations on fuel economy are being introduced in various countries and reducing CO2 emissions has become mandatory. Europe leads in terms of enhanced regulations and other countries are being asked to follow suit. The target fuel economy for passenger cars in Europe in 2021 is set at 95g/km. Even more stringent target of 68 to 78g/km is being proposed for 2025.



Future aspect of automotive powertrain

 According to the prediction of new passenger cars published by the International Energy Agency (IEA) (see below), electrified vehicle technology will bring in more electrified vehicles on the road. Most vehicles will be built by electrified vehicle technology in 2050 and vehicles powered by an ICE will account for about 10%. However, genuinely electrified vehicles such as EVs and FCVs will only account for 50% or so of all automobiles in 2050. The number of hybrid vehicles (HVs/HEVs) and plug-in hybrid vehicles (PHVs) will continue to increase but they will still be fitted with an ICE. In other words, vehicles fitted with ICEs will account for one half or more in 2050. This shows that efforts to improve fuel economy of ICEs must go on through the future. This assumption runs in all lectures by the four carmakers summarized below in predicting the future of powertrains.

Outlook of electrified vehicles in the future
Source: Nissan Motor Co., Ltd.



Toyota: Direction of future powertrain development

Mr. Terutoshi Tomoda Key future technologies for engines
Terutoshi Tomoda, General Manager Advanced Engine Design & Engineering Div. Unit Center, Toyota Motor Corporation Created by MarkLines based on materials from Toyota Motor Corporation


 Mr. Terutoshi Tomoda, Manager, Advanced Engine Engineering, Unit Center of Toyota Motor Corporation, spoke about the direction of technical development of powertrains for automobiles in the future. He mentioned three areas that needed improvement; thermal efficiency, fuel, and driving performance, that could be achieved by three key technologies addressing (1) lean burn, (2) variable compression ratio and (3) fuel reforming.

Increased max, thermal efficiency by supercharged lean burn
Created by MarkLines based on materials from Toyota Motor Corporation

 Unlike the current Prius that uses cooled EGR, Toyota is reforming its NA engines by using a large-volume cooled EGR. To increase thermal efficiency to 40% or higher, enhanced combustion, reduction of cooling loss and supercharged lean burn have been proven effective. By combining these technologies, Toyota has already achieved the maximum thermal efficiency of 44% in laboratory.

Variable compression ratio
Source: Toyota Motor Corporation

 By adjusting variable compression ratio is a technology to adjust the compression ratio to optimal values under varying loads from low to high. a vehicle can expand the range in which the engine can operate at high efficiencies.

 The optimal variable compression ratio can be achieved by a number of technologies including a multilink mechanism (Daimler), dual piston mechanism (Honda), variable-length connecting rod (FEV) and variable compression ratio cylinder head (SAAB). Toyota is also testing several original technologies to achieve variable compression ratio.

 In 2011, Toyota Central R&D Labs, Inc., published the results of studies on fuel reforming using an EGR system. The company added fuel to exhaust gas to reform the fuel before it was sent to the combustion chamber. In this way, the company succeeded in increasing the speed of combustion and improving the thermal efficiency.

 Mr. Tomoda states that engines will remain the main powertrain in 2025. Engines will be subject to various demand from customers and available energy sources in different regions. To meet such demand, future engines are required to achieve raised ceiling of maximum thermal efficiency, expanded zone of high thermal efficiency and compatibility with a broad variety of fuels. Toyota will meet demands for higher thermal efficiencies and fuel compatibility by supercharged lean burn and combustion control, optimal variable compression ratios and fuel reforming.



Nissan: Our tasks to make ICE survive in coming century

Mr. Ryozo Hiraku
Mr. Ryozo Hiraku, Alliance GM Powertrain Advanced Engineering Department, Powertrain Engineering Division Nissan Motor Co., Ltd.

 Mr. Ryozo Hiraku, Alliance GM, Advanced Powertrain Technical Engineering HQ, Powertrain Development HD of Nissan Motor Co., Ltd., spoke on the theme of "Our tasks to make ICE surviving in the coming century." Nissan thinks that EVs will be the mainstream automotive technologies in the future although all vehicles will not be replaced by EVs overnight. Consequently, Nissan feels that further evolution of ICE powertrain is still important.


Evolution of energy efficiency
Source: Nissan Motor Co., Ltd.

 Evolution of energy efficiency of internal combustion engine If ICEs are to continue to play an important role during the next hundred years, an ICE for average passenger cars should have an energy efficiency of 60% in 2100.

 It is interesting to imagine future performance of ICEs if they are to continue to evolve for another hundred years. The graph above shows the evolution of energy efficiency over the past hundred years. It increased very slowly from 18th to 19th century. The graph shows a sharp rise over the last fifty years from 1850. If the thermal efficiency keeps rising at the same rate for another hundred years, it could reach 60% by around 2100 in Nissan's bold prediction.


An ICE having achieved energy efficiency of 60%
Source: Nissan Motor Co., Ltd.

 The state of an ICE with energy efficiency of 60% may be represented by an energy efficiency map above in terms of compression ratio and cooling loss (shown in color gradations). Improved energy efficiency cannot be expected from a higher compression ratio alone. According to Nissan's studies, energy efficiency could be increased by a combination of reduced cooling loss and higher compression ratio.

 Cooling loss may be reduced by using highly responsive heat insulation film, insulation materials, etc. An approach to improve compression ratio may seek ideal combustion of air-fuel mixture in an ultra-lean condition. This may be achieved through diluted combustion (including Homogeneous Charge Compression Ignition: HCCI) in which the air-fuel mixture is mixed thoroughly to leave no unburnt mixture), addition of hydrogen, fuel reforming, variable compression ratio mechanism, etc.


Change in average fuel economy of passenger cars Driving at fuel economy of 100km/liter in 10-15 mode

Change in average fuel economy of passenger cars (in 10-15 test method). Fuel economy of passenger cars is increasing constantly at an annual average of 2.5% -----:Average fuel economy of all passenger cars

Source: Nissan Motor Co., Ltd.
Created by MarkLines based on materials from Nissan Motor Co., Ltd.

 The average fuel economy of gasoline-fueled passenger cars is increasing at an average rate of 2.5% a year (in a 10-15 test method) over the past 20 years. If it keeps evolving at the same rate, the average fuel economy of passenger cars will top 100km/liter in 2080. The meaning of fuel economy of 100km/liter may be explained as the following: Driving at fuel economy of 100km/liter in 10-15 test mode (4.16km) will consume approx. 42cc of fuel. 42cc of gasoline has approx. 1.5MJ of energy, only equivalent to heat needed to raise the temperature of 50kg of aluminum by 30 degrees Celsius. In other words, thermal energy of gasoline fuel is spent entirely, and not even enough, to heat the ICE itself before we can discuss the efficiency of converting thermal energy into kinetic energy. According to the speaker, this indicates that even the heat consumed when idling a cold engine must be reduced to the utmost limit.

 Mr. Hiraku summarized technical development that needs to be challenged now. Continuing exploration of ultimately high thermal efficiency will require technical development of highly responsive heat insulation film and material to reduce cooling loss, ultra-lean combustion (including HCCI) and addition of hydrogen to increase compression ratio, and variable compression ratio mechanisms to achieve ultra-high expansion ratio. All-out reduction of thermal capacity will require new structures that will use large amounts of lightweight and high-strength materials to reduce the overall weight, and heat insulation of combustion chambers by using heat insulation materials and films to reduce heat spent for warming the engine. This will also require development of thermal conductivity and directivity variable components and low-temperature combustion technologies.



Honda: Progress in development of ICE technologies

Mr. Ayumu Matsuo
Mr. Ayumu Matsuo, Operating Officer Chief Officer of Development Strategy for Power train, Automobile R&D Center, Honda R&D Co., Ltd.

 Mr. Ayumu Matsuo, corporate officer in charge of powertrain strategy, Automobile R&D Center, Honda R&D Co., Ltd., spoke on the subject of "Progress in the development of internal combustion engines."


Key areas for improving fuel economy
Created by MarkLines based on materials from Honda R&D Co., Ltd.

 Improving the thermal efficiency of the engine is the primary approach toward higher fuel economy. This may be achieved by increased compression ratio, exhaust heat recovery, low-temperature combustion, heat insulation, etc. Thermal efficiency may also be improved by increasing the transmission efficiency of drivetrain and expanding the gear ratio range. The third approach is to reduce the driving energy of the body. Higher thermal efficiency may also be achieved by electrification technologies addressing higher efficiency of HEV systems and deceleration energy regeneration on vehicles with ICEs.


Ideal image of engines
Created by MarkLines based on materials from Honda R&D Co., Ltd.

 The evolution of ICEs toward higher fuel economy and driving performance is synonymous to the evolution of thermal efficiency, exhaust heat recovery and output density. The likely key technologies toward this roadmap are lean burn, supercharging and diluted combustion using large-volume EGR (ideal combustion achievable by thoroughly mixing the air-fuel mixture in the cylinder). Honda aims to increase thermal efficiency by low-NOx lean burn based on Homogeneous Lean Charge Spark Ignition (HLSI) combustion consisting of spark ignition and HCCI.


Weight reduction leads to further weight reduction
Created by MarkLines based on materials from Honda R&D Co., Ltd.

 Downsizing of powertrain will lead to the weight reduction of the body. Further weight reduction can be achieved by downsizing and sound design of the chassis components. This will lead to light body weight which, in turn will allow further downsizing of the powertrain, thus creating a positive spiral effect of weight reduction.

 Mr. Matsuo noted that sales of EVs and FCVs will increase steadily and technical development toward electrification is important for automakers. However, he continued, problems remain for the energy infrastructures for electric vehicles and fuel cell vehicles. Therefore, vehicles powered by ICEs will keep increasing until about 2040 to meet the globally expanding demand for automobiles and the evolution of ICEs is the key to reducing the CO2 emissions.



Mazda: Future prospects of advanced ICEs for passenger cars

Mr. Toshihide Yamamoto
Mr. Toshihide Yamamoto, General Research Manager Power Source Research Field Technical Research Center Mazda R&D Co., Ltd.

 Representing Mazda Motor Corporation, Mr. Yoshihide Yamamoto, manager, next generation powertrain research dept., Mazda R&D Co., Ltd., spoke on the subject of "the concept of evolution of internal combustion engines for passenger cars."


Basic concept of improving thermal efficiency
Created by MarkLines based on materials from Mazda

 To improve fuel economy is to reduce losses. Exhaust loss and cooling loss are the two major elements in improving thermal efficiency. Other losses are mechanical loss and pumping loss. Compression ratio, specific heat ratio, combustion time, combustion timing, surface heat transfer, pressure difference between intake and exhaust strokes, and mechanical resistance are the seven controllable factors in reducing these losses. Improving fuel economy is an attempt to improve all those controllable factors.


 In the 1st Step SKYACTIV-G for gasoline engines, Mazda attempted to improve fuel economy by introducing higher compression ratio and delayed valve closing (Miller cycle) and reducing mechanical resistance. In the 2nd Step SKYACTIV-G, further improvement is being attempted through introducing still higher compression ratio and lean HCCI, further reduction of mechanical resistance, etc. In the 1st Step and 2nd Step SKYACTIV-D for diesel engines, Mazda is striving to improve fuel economy through introducing lower compression ratio, optimization of combustion period and timing, reduction of mechanical resistance by load reduction, etc. In the 3rd Step of SKYACTIV technology, Mazda will challenge reduction of cooling loss in both gasoline and diesel engines. Both gasoline and diesel engines will be routed to the same goal in the long run.


 To gain better understanding of phenomena related to the reduction of cooling loss, Mazda is conducting coupled analysis of combustion and heat transfer, measurement of instantaneous thermal flux of insulation wall, near-wall gas temperature and flow rate, etc. The company is conducting boundary area heat transfer analysis, detailed calculation of chemical reaction and multiscale analysis to analyze the effect upon heat transfer area, heat transfer coefficient, gas temperature and combustion chamber wall temperature to understand phenomena related to cooling loss reduction.


fuel economy well-to-wheel CO2 emissions
Source: Mazda Created by MarkLines based on materials from Mazda

 In 1st Step SKYACTIV and 2nd Step SKYACTIV technologies, Mazda sought higher specific fuel economy through introduction of higher compression ratio and lean burn. In 3rd Step SKYACTIV, the company is seeking still higher fuel economy through reduction of cooling loss.

 As the final goal of the SKYACTIV engine technologies, Mazda is striving to reduce the CO2 emissions to half the level of 1st Step. When combined with the reduction of vehicle's driving work load, this is equivalent to the well-to-wheel CO2 emissions of EVs.

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