Multi-mode 2-stroke/4-stroke internal combustion engine

Abstract

In a multi-mode, 2-stroke / 4-stroke internal combustion engine operation, by switching the engine stroke from 4-stroke operation to 2-stroke operation so that the combustion frequency is doubled, doubling of the engine power is achieved even at the same work output per cycle. In order to meet the demand of extremely high power, the engine operates in 4-stroke boosted SI operation transitioned from 2-stroke HCCI operation at pre-set level of power and crank speed requirements. By combining the multi-stroke (2-stroke HCCI and 4-stroke HCCI) and multi-mode operation (2-stroke HCCI and 4-stroke boosted SI operation), full load range and overall high efficiency with minimal NOx emission are achieved.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a multi-mode, 2-stroke / 4-stroke internal combustion engine operation which maximizes efficiency and power, while minimizing emission.[0003]2. Description of Related Art[0004]Spark Ignition (SI) engines, which are widely used in United States in passenger vehicles, suffer from low efficiency in comparison to Compression Ignition (CI), or Diesel engines, especially in a partial load due to throttling. CI engines, however, exhibit high particulate and NOx emissions characteristics due to their combustion nature. Recently, Homogeneous Charge Compression Ignition (HCCI) engines have been introduced, which have higher efficiency comparable to CI engines as well as minimum particulate and NOx emissions characteristics, with the versatility of using gasoline as well as diesel fuel.[0005]In HCCI engines, a spark plug or a high-pressure injector is not used for initiation of the ignition of the fu...

AI Technical Summary

Benefits of technology

[0010]Another objective of the present invention is to provide an internal combustion engine which achieves the extremely high load range with smooth transition and maintains high efficiency.

[0011]In accordance with the present invention, the intrinsic load limitation of HCCI is overcome by switching the engine stroke from 4-stroke (“4S”) to 2-stroke (“2S”) so that the combustion frequency is doubled and hence, even at the same work output per cycle, the engine can double the power which is comparable to that in the conventional SI / CI engines. Although this stroke switching of the present invention produces about the similar power range as the mode switching from 4S HCCI to 4S SI does, the differences are in the emission and efficiency. HCCI operation is inherently clean and efficient combustion even in 2S operation. Additionally, the stroke switching between the same combustion strategies is much simpler and smoother than the mode switching between the different strategies. Consequently, the stroke switching is superior to mode switching.

[0012]To operate in 2S HCCI mode, the followings are required: The first is the flexible valve system such as Electro-Hydraulic Valve System (EHVS) or cam-phaser to operate at different valve profiles for stroke switching between 2S to 4S HCCI. Secondly, a super charger or combination of turbo and super chargers to boost the intake manifold to enable fast gas exchange for 2S operation. It is noteworthy that in 2S HCCI, the complete scavenging is not required because large portion of the exhaust gas is used in the next cycle, which makes the system and control simpler than in a hybrid of 4S / 2S SI which has additional intake system for 2S operation as seen in U.S. Pat. No. 5,007,382, for example. In the present invention, a slight modification in the intake valve may be required to enhance the flow motion for fast gas exchange process. Finally, the direct injection system is required to precisely control the HCCI combustion and prevent the short-circuiting of the intake charge in 2S operation.

[0013]In order to meet the demand of the extremely high power, in present invention the engine operates on 4S boosted SI transitioned from 2S HCCI at pre-set level of power and crank speed requirements. Having the flexible valve system, supercharger or combined with turbo charger, and direct injection system allows the full controllability on smooth transition from 2S HCCI to 4S boosted SI. 4S boosted SI produces up to 40-80% more power than 2S HCCI operation in the present invention. In summary, by combining the multi-stroke (2S HCCI and 4S HCCI) and multi-mode operation (2S HCCI and 4S boosted SI), full load range and overall high efficiency with minimal NOx emission may be achieved in comparison to conventional SI or SI / HCCI strategies.

Problems solved by technology

Spark Ignition (SI) engines, which are widely used in United States in passenger vehicles, suffer from low efficiency in comparison to Compression Ignition (CI), or Diesel engines, especially in a partial load due to throttling.

CI engines, however, exhibit high particulate and NOx emissions characteristics due to their combustion nature.

However, the limited work output is one of the major challenges in HCCI operation, which limitation is caused by the high dilution of mixture in the cylinder.

The dilution with hot exhaust gas is not only required to increase the mixture temperature to achieve auto-ignition, but also required to limit the high rate of pressure rise, which otherwise would be destructive to the engine components.

However, in this case, the emission and efficiency benefits of HCCI operation are lost in the medium to high load range, and the transient combustion control of HCCI in mode switching is not a subtle issue in current research and industries.

Secondly, boosted HCCI may give higher power, but it is also limited since the combustion becomes too noisy and destructive due to the high rate of pressure rise from rapid burn rate.

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