Research on revolutionary combustion technology: Contemplating the limits of innovation

Nissan's variable compression ratio technology and Volkswagen's latest 1.4L TDI engine

2016/11/25

Summary

SIP challenge
(* SIP challenge "Innovative combustion technology": Combustion visualized with laser beams)

  Research on combustion engines will go on through 2050. According to a prediction by the International Energy Agency, the percentage of internal combustion engine vehicles (ICEVs) in global vehicle sales will drop to 55% in 2050. However, automakers around the world are competing fiercely to improve the fuel efficiency of ICEVs. Toyota Motor Corporation is investigating all possibilities for these engines in its development processes. Honda Motor Co., Ltd. is pursuing engine development together with technologies for downsizing, plug-in hybrid vehicles, and electrification. Infiniti, a brand of Nissan Motor Co., Ltd., is developing a turbocharger with variable compression ratio technology (VC-Turbo). Mazda Motor Corporation is advocating right-sizing in its pursuit of ICEV development under a slogan of right sizing.

  In Japan, AICE (The Research association of Automotive Internal Combustion Engines) was formed based on the model of a European consortium. AICE aims to achieve a thermal efficiency of over 50% for gasoline and diesel engines through cooperation between industry, universities, and the government. In Europe, Real Driving Emissions (RDE) testing is scheduled to begin in 2017. Volkswagen AG, the General Motors Group company Adam Opel AG, and other OEMs announced that the displacement of their engines will be increased to improve exhaust gas and fuel economy during actual driving. Meanwhile, Daimler AG unveiled its intention to focus on Connectivity-Autonomous-S hared-Electric (CASE) technology at the 2016 Paris Motor Show and has started strategically shifting its emphasis to the development of electric vehicles. Volkswagen management has stated its intention of concentrating the company's efforts on developing battery electric vehicles (BEVs). European OEMs will accelerate the development of BEVs at the expense of fuel cell vehicles (FCVs). This report will describe AICE's achievements, Nissan Infiniti's VC-Turbo technology, and Volkswagen's latest downsized engine.

Note) *SIP:Cross-ministerial Strategic Innovation Promotion Program
In June 2016, an open lab (explanation of research and laboratory tour) was conducted at Keio University's SIP engine laboratory in Ono Sokki's Technical Center).


Related Reports:

Automotive technology on the road to 2050: ICEV, electrification, PHV, FCV, weight reduction, and ADAS (Oct. 2016)
Volkswagen Passat teardown (1): 1.4L turbo-gasoline engine (Oct. 2016)
Evolution of the internal combustion engine (Feb. 2016)

JSAE Exposition 2015:
Envisioning future of powertrains for passenger cars (1) Trends in Japan (Jun. 2016)
Envisioning future of powertrains for passenger cars (2) Trends in Europe (Jun. 2016)



SIP challenge for "Innovative combustion technology" : Raising the maximum thermal efficiency of gasoline and diesel engines to 50%

  AICE was formed in 2014. It consists of nine Japanese automakers and two research institutes. More than two years have passed since its formation, and AICE has started to yield a number of results. "Revolutionary combustion technology" is one of 11 SIP challenges, and teams tasked with working on gasoline combustion, diesel combustion, loss reduction, and controls were organized across universities in Japan to address it. The four teams actively research their areas in cooperation with automakers and patron companies. This section outlines an open lab that was held at Keio University's SIP engine laboratory in Ono Sokki Co., Ltd.'s Technical Center.

Numerical target

  Engine thermal efficiency improved by 10% over a period of about 40 years from the 1970s to around 2010. Research activity is under way with an ambitious target of achieving a further 10% improvement in five years starting from 2014.

Numerical target
(Source: Created by MarkLines based on materials provided by Professor Norimasa Iida of Keio University Graduate School)



Results: Gasoline Team achieves thermal efficiency of 45% and Diesel Team identifies possibility of smokeless combustion

Results
(Source: Created by MarkLines based on materials of Professor Norimasa Iida at Keio University Graduate School)

  In June 2016, the Gasoline Combustion Team achieved an indicated thermal efficiency of 45% for a single-cylinder engine. The figure is 4 points above the highest thermal efficiency (41%) of gasoline engines that are currently mass-produced. An excess air factor λ as lean as 1.89 was achieved in the air-fuel mixture of the engine (traditional excess air factor λ = 1.0). This is called super lean burn.

    Increasing compression ratios in lean excess air factor conditions normally entails the following problems:
  • The mixture fails to ignite;
  • Even if the mixture ignites, it goes out;
  • The engine knocks; and
  • Heat escapes through the wall of the combustion chamber.

Consequently, super lean burn has proved difficult.

    The Gasoline Combustion Team has achieved an indicated thermal efficiency of 45% through improvements including:
  1. Powerful ignition system: The air-fuel mixture ignites properly even with a mixture flow rate of 20 m/s or greater;
  2. High-efficiency tumble intake port: With an improvement in the combustion chamber, the turbulence intensity of the air-fuel mixture is set at 5 m/s or greater to enhance flame propagation;
  3. Temperature control for combustion chamber: This prevents engine knock even under a compression ratio greater than 15;
  4. Refinement in combustion chamber surface geometry: Low-temperature combustion reduces cooling loss by 50%.

Results
(Source: Created by MarkLines based on materials of Professor Norimasa Iida at Keio University Graduate School)

  The Diesel Combustion Team has identified the possibility of smokeless combustion by using injection with a high pressure of 350 MPa. The acceleration of combustion was not achieved under a conventional injection pressure of 200 MPa because that level of pressure causes a large amount of residual soot. An extreme injection pressure of "350 MPa" has been found to be effective in speeding up combustion and making the mixture leaner in the combustion area. The Loss Reduction Team has started to yield results including the identification a coefficient of piston skirt friction that can be reduced as low as 0.007 at the test-piece stage.

Results
(Source: Created by MarkLines based on materials of Professor Yasuhiro Daisho at Faculty of Science and Engineering, Waseda University)


Nissan Infiniti's VC-Turbo: The world's first production-ready variable compression ratio engine

"VC-Turbo (Variable Compression-Turbocharged)"

  In September 2016, Nissan Motor Co., Ltd. unveiled the world's first variable compression ratio mechanism at the Paris Motor Show. This innovative engine technology uses a multi-link system that can seamlessly change the height of the top-dead-center of the pistons in accordance with the car's driving condition and driver inputs. It can vary its compression ratio (volume ratio) anywhere from 8:1 (high performance) to 14:1 (high efficiency). The VC-Turbo 2.0-liter four-cylinder engine generates a maximum output of 200 kW (268hp/272ps) and a maximum torque of 390 Nm to match the performance of and exceed the efficiency of six-cylinder gasoline engines. The VC-Turbo engine achieves low levels of noise and vibration, and is lighter and more compact than high-output V6 engines. This technology represents a major and historical breakthrough in the development of internal combustion engines. The engine will be used in new Infiniti models scheduled for release in 2018.
VC-Turbo
VC-Turbo    VC-Turbo
(Source: Infiniti's press releases)


  The bottom left of the image above shows the multi-link mechanism that sets the compression ratio at 14. Generally, a high compression ratio permits high thermal efficiency and good mileage. When the compression ratio is set at 14.0, the system burns the air-fuel mixture in the Miller cycle. The bottom right of the image above shows the multi-link mechanism that sets the compression ratio at 8. When in this state, the system burns the mixture in an Otto cycle. Typical turbo engines generate high output by causing the turbocharger to thrust a large volume of air into the combustion chamber when the compression of the air-fuel mixture is low (compression ratio: 8.0).

  With reference to the bottom right of the image, turning the Harmonic Drive in the direction of (1) moves the actuator arm in the direction of (2) and changes the multi-link angle to that shown in the bottom left of the image. This motion raises the height of the top-dead-center and sets the compression ratio at 14:1.

  The drawing below illustrates the multi-link structure. When deep blue Harmonic Drive (1) rotates counterclockwise, control shaft (2) indicated with the red circle rotates counterclockwise around the eccentric linkage center (A). As a result, the center of control shaft (2) moves downward (as indicated with (3)), and the compression ratio becomes greater. Conversely, when Harmonic Drive (1) rotates clockwise, control shaft (2) rotates clockwise. As a result, the center of control shaft (2) moves upward (as indicated with (4)), and the compression ratio becomes smaller.


[Multi-link construction for variable compression ratio]


(Source: Created by MarkLines based on Infiniti's press releases)

[Infiniti VC-Turbo engine specifications]

Fuel type Gasoline
Construction Aluminum block with mirror coating to cylinder bores, aluminum cylinder head with integrated exhaust manifold, single-scroll turbocharger with intercooler
Compression ratio 8.0:1 to 14.0:1
Capacity 2.0-liters, 1,997 to 1,970 cc (8.0:1 to 14.0:1)
Cylinders 4
Valves 16 (four per cylinder)
Valve control Intake: Electronic Variable Valve Timing Control
Exhaust: Hydraulic Variable Valve Timing Control
Turbo Single-scroll turbocharger with electronic wastegate actuator
Turbo cooling Intercooler
Fuel system Gasoline direct injection (DIG) and/or multi-point injection (MPI)
Max power 200 kW (267 hp / 272 ps)
Max torque 390 Nm (288 lb ft)
(Source: Created by MarkLines based on Infiniti's press releases)


Volkswagen's newest gasoline engine: Next-generation TSI gasoline turbo engine features increased displacement

  Volkswagen announced a 1.5-liter TSI gasoline engine, a larger displacement version of its mainstay 1.4-liter TSI, at the International Vienna Motor Symposium in April 2016. With this new engine, the automaker aims to improve the fuel economy and emissions performance of its vehicles in response to Real Driving Emissions (RDE) testing, which is scheduled to begin in Europe in 2017. Under hard acceleration or heavier engine loads, the 1.5-liter engine allows the throttle valves to be opened less widely than the 1.4-liter engine. This is the same concept as Mazda's right sizing. The 1.5-liter engine, which is named the EA211 TSI evo, uses a turbocharger with variable turbine geometry, a first for volume-produced engines. The new TSI evo also features a compression ratio of 12.5:1, cylinder deactivation, common-rail injection system with up to 350 bar pressure, plasma spray-coated cylinder walls, and up to 10% improved fuel efficiency in the Miller cycle. The TSI evo engine will be available in two power outputs; 130 ps and 150 ps.

  The new TSI evo engine is expected to replace the existing lineup of EA211 TSI engines that have been available for the company's key models since 2012.

EA211 TSI engines
Type In-line four-cylinder DOHC
16-valve IC turbo
Remarks
Engine name CZR (EA211 TSI): Existing model EA211 TSI evo (2016 model)
Total engine displacement 1394 cc 1498 cc Longer stroke for displacement expansion
Bore × stroke (mm) 74.5 × 80.0 74.5 × 85.9
Compression ratio 10 12.5 Note (3) Miller cycle with increased compression ratio
Max. power 150 ps 130 ps 150 ps (details yet
to be announced)
Max. torque 25.5 kg-m 20.4 kg-m
Fuel supply method Electronic control
Supercharger Turbo with intercooler VTG turbocharger
with intercooler (1)
Turbo with variable turbine geometry (for volume-produced engines)
Fuel used Unleaded premium gasoline
Variable valve mechanism Variable intake and exhaust valve timing
Cylinder deactivation (ACT evo)
APS coating (2) No Yes Cylinder walls coated in plasma spray
Injector with up to 350 bar pressure Conventional method Yes Highly pressurized
Combustion cycle Otto Miller cycle
Map-controlled cooling module Conventional method Yes
Notes (1) Variable turbine geometry (VTG): The system uses an electric actuator to move intake blades installed in front of the exhaust-gas turbine and thereby adjusts the flow rate of exhaust gas to the turbine. Although Porsche uses VTG on the 911 Turbo, the new TSI evo is the first to make the technology accessible in mass-production vehicles. The system allows the turbine to be turned fast even in a low speed range.
(2) APS (atmospheric plasma spray): Cylinder liners are coated using the plasma spray process in atmospheric conditions.
(3) As for the 150ps model, advance notice was only given at this announcement.

(Source: Created by MarkLines based on Volkswagen's press releases)


  In Europe, RDE testing is scheduled to begin in 2017. Volkswagen, the General Motors Group company Adam Opel, and other OEMs announced that the displacement of their engines will be increased to improve emissions performance and fuel economy in actual driving.

  Daimler unveiled its intention of focusing on CASE at the 2016 Paris Motor Show and has started a strategic shift of emphasis to the development of electric vehicles. Volkswagen management has stated its intention of concentrating the company's efforts on developing BEVs. European OEMs will accelerate the development of BEVs at the expense of FCVs.

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Keyword:
ICEV, Electrification, PHEV, FCV

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