Atkinson Cycle Method:
Conventional 4-stroke and 2-stroke engines have reached their limits in terms of thermal efficiency. Large 2-stroke diesel engines can achieve up to 48% thermal efficiency but at the cost of increased pollution. Four-stroke diesel engines typically achieve 28-42% thermal efficiency, while 4-stroke gasoline engines reach about 25%. Simulating the Atkinson cycle within Otto or diesel cycles 4-stroke engine has the potential to improve heat engine thermal efficiency between 12 to 27%.
The Atkinson cycle is a unique method for increasing combustion engine thermal efficiency by lowering the compression ratio relative to the expansion ratio. Modern 4-stroke engine technology can switch between the Otto or diesel cycle and the Atkinson cycle using variable valve timing mechanisms.
Problems with Conventional Combustion Engines:
Conventional 4-stroke engines can simulate the Atkinson cycle by using late intake valve closing (LIVC). However, this method introduces “parasitic pumping losses” that reduce efficiency and performance. LIVC extends the intake valve closure past top dead center (TDC) into the compression stroke. During this phase, the upward movement of the piston partially expels intake air from the combustion chamber back into the intake manifold. Consequently, the engine must expend mechanical energy to draw air from the intake manifold into the combustion chamber during the intake stroke and additional energy to pump some of the same air out during the early compression stroke. These parasitic pumping losses increase as the prominence of the LIVC Atkinson cycle grows, resulting in only modest improvements in thermal efficiency compared to the Otto or Diesel cycles.
Another drawback of simulating the Atkinson cycle with LIVC is its incompatibility with forced induction systems. During the compression stroke, the reversal of intake air flow works against the intended benefits of turbochargers or superchargers, which are designed to increase intake air density and boost performance and efficiency. Modern diesel engines, for instance, depend heavily on turbochargers for sufficient power generation. Since the LIVC Atkinson cycle gains little benefit from forced induction, 4-stroke engines utilizing this approach are primarily used in niche hybrid vehicles. In these applications, the reduced power output of the LIVC Atkinson cycle is compensated by the electric motor.
Dynamic Flow Engine’s Atkinson Cycle Enhancing Efficiency:
Another method for simulating the Atkinson cycle is early intake valve closing (EIVC). This approach involves closing the intake valve early during the intake stroke, cutting off the flow of intake air into the combustion chamber from the intake manifold. By avoiding the additional pumping work required in the LIVC Atkinson method, the EIVC approach eliminates the parasitic pumping losses associated with LIVC.
A Dynamic Flow engine utilizing the EIVC Atkinson cycle requires significantly less mechanical energy for pumping intake air compared to Otto and Diesel cycles. Among these cycles, the conventional 4-stroke LIVC Atkinson cycle demands the most mechanical energy for intake air pumping, while the Dynamic Flow engine EIVC Atkinson cycle requires the least. This reduced energy requirement allows the Dynamic Flow engine operating with the EIVC Atkinson cycle to achieve much greater thermal efficiency than conventional 4-stroke engines using the LIVC method.
Unlike the LIVC method, the EIVC Atkinson cycle does not require intake air to be expelled from the combustion chamber during the compression stroke. This eliminates reverse intake air flow, avoiding conflicts with the operation of turbochargers and superchargers. As a result, the Dynamic Flow engine operating on the EIVC Atkinson cycle can fully benefit from forced induction systems, much like Otto and Diesel cycles. Furthermore, Dynamic Flow engines running on Otto or Diesel cycles can seamlessly switch to EIVC Atkinson cycle mode while maintaining the active use of turbochargers and superchargers.
Despite its advantages, the EIVC Atkinson cycle method is not widely adopted in conventional engines. This limitation arises from the physical interference between the piston head at top dead center (TDC) and the intake valve in its open position, making EIVC incompatible with current conventional 4-stroke Otto or Diesel engines. Additionally, the inherent characteristics of the 2-stroke engine cycle prevent it from simulating the Atkinson cycle altogether.
The unique valve configuration of the Dynamic Flow engine overcomes these limitations, enabling it to simulate the Atkinson cycle using EIVC.
Core Advantages of Simulating the Atkinson Cycle with EIVC:
The Dynamic Flow engine’s distinct valve configuration enables the use of an EIVC Atkinson cycle within both gasoline (Otto) and diesel cycles. A Dynamic Flow engine operating on the EIVC Atkinson cycle offers significantly greater thermal efficiency compared to conventional 4-stroke LIVC Atkinson cycle engines. When paired with a turbocharger, the Dynamic Flow engine achieves improved performance, surpassing current 4-stroke LIVC Atkinson cycle engines. This combination of higher efficiency and performance makes the Dynamic Flow engine with the EIVC Atkinson cycle suitable for a wide range of applications beyond the niche hybrid vehicle market, expanding its benefits to broader transportation sectors.
Simulating the EIVC Atkinson cycle in Dynamic Flow gasoline and diesel engines can further boost thermal efficiency by an additional of 10 to 27% on top of the existing 48%. This would enable the Dynamic Flow 4-stroke engine to achieve up to 75% thermal efficiency, a level that current 4-stroke and 2-stroke engines struggle to reach, rarely exceeding 50%. This innovative approach also supports multi-fuel compatibility, allowing the engine to easily adapt to future fuel types such as synthetic fuels, ammonia, and hydrogen.