|Nissan uses VVEL’s control of valve timing and lift to control temperature by using internal EGR in its HCCI development. Click to enlarge.|
During its recent Advanced Technology briefings in Japan, Nissan provided a general overview of its development of HCCI (homogeneous charge compression ignition) combustion engines. Nissan says it intends to roll out HCCI with the goal of reducing engine CO2 emissions by 30% from the current level by 2015. The work is part of Nissan’s Green Program 2010.
An HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder, producing a low-temperature, flameless release of energy throughout the entire combustion chamber. All of the fuel in the chamber is burned simultaneously. Using a lean pre-mixed air-fuel mixture and keeping flame temperatures low helps keeps NOx and particulate production low. The lean-burn HCCI engine is a very good candidate for future clean and economical passenger vehicle applications, and automakers project significant cuts in CO2 emissions resulting from their use.
|Extending the range of HCCI combustion is one of the development challenges. Click to enlarge.|
However, HCCI combustion is difficult to control, and currently automakers have succeeded in operating in HCCI mode only in a limited range. Expanding that operating range is one of the key challenges. (In May, GM demonstrated gasoline HCCI at idle, a significant extension. Earlier post.)
Nissan highlighted three tools and mechanisms it is using in its pursuit of HCCI. First, is in-cylinder temperature measurement. To accurately measure the gas temperature inside the combustion chamber, Nissan and Stanford University jointly developed technology to measure the real-time gas temperature inside the engine.
To control the temperature of the gas in the chamber Nissan uses its VVEL system. VVEL allows free control of the valve timing and lift for both intake and exhaust valves and thus manages the gas temperature inside the combustion chamber by altering the amount of EGR according to driving conditions.
Nissan has also developed a HCCI combustion simulation system which creates a high-speed three-dimensional representation of the chemical reactions in the HCCI combustion process.
HCCI combustion is a complex process of chemical reactions involving thousands of reaction formulae. Existing HCCI simulation can take up to 2 months to simulate such combustion processes in detail, making practical application to engine development difficult.
Nissan’s newly developed technology enables approximately 20 times faster HCCI simulation, utilizing the company’s accumulation of combustion data and combustion modeling technology. This large reduction in computation time—shrinking 2 months to approximately three days—enables practical application to engine development, Nissan said.
|Output from Nissan’s combustion simulation system. To the left is a frame from a 3D animation. To the right is a plot of calculated results versus actual figures. Click to enlarge.|
Tsuyoshi Matsuda, Tomonori Urushihara, Takeshi Nakamura, Hiroki Wada, Toshiya Kono (Nissan Motor Company , Ltd.) A Study of Gasoline-fueled HCCI Engine—Mode Changes from SI Combustion to HCCI Combustion (SAE 2008-01-0050)
Akihiko Kakuho, Morihiro Nagamine, Yukio Amenomori, Tomonori Urushihara, Teruyuki Itoh (Nissan Motor Co., Ltd) In-Cylinder Temperature Distribution Measurement and Its Application to HCCI Combustion (SAE 2006-01-1202)