Squish Piston Otto Engine Miller Cycle Efficiency
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Solution Overview
Problem
Stationary Otto gas engines face limitations in efficiency and pollutant emissions due to high thermal loads, high system costs, and maintenance requirements, particularly when operated with stoichiometric combustion and three-way catalytic converters, and compromise engine parameters when using lean burn processes without exhaust treatment.
Innovation Solution
The method involves designing the Otto gas engine with a squish piston and operating it under a Miller cycle with reduced swirl numbers and optimized intake port designs, advancing intake valve closure to reduce gas exchange work, enhance turbulence, and increase compression ratio, while using a lean combustible gas-air mixture or stoichiometric combustion with exhaust gas recirculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the Otto gas engine is operated with stoichiometric combustion and a three-way catalytic converter, then pollutant emissions can be treated effectively, but the thermal load on engine components increases and system costs rise
Solution Approach 1:
The invention changes the operating parameters by using lean burn combustion (excess air) instead of stoichiometric combustion, and implements early intake valve closing to reduce compression ratio and peak temperatures. This allows effective pollutant treatment without the high thermal loads associated with stoichiometric operation and three-way catalytic converters.
Solution Approach 2:
The invention extracts or removes the three-way catalytic converter from the exhaust system by using lean burn combustion with EGR, which inherently produces lower pollutant levels that do not require expensive aftertreatment, thereby reducing thermal load on components.
2Temperature
If the Otto gas engine is operated with homogeneous lean burn process without exhaust gas aftertreatment, then thermal load is reduced, but engine efficiency is limited due to compromise in engine parameters
Solution Approach 1:
The invention performs preliminary action by closing the intake valve early in the intake stroke (before BDC), which pre-limits the amount of charge entering the cylinder. This allows the engine to operate with lean burn combustion without requiring expensive exhaust aftertreatment, while maintaining good efficiency through optimized charge management and turbulence control.
Solution Approach 2:
The invention introduces dynamic control of the intake valve timing, closing it at an optimized crank angle position that varies with operating conditions. This dynamic adjustment allows the engine to maintain high efficiency across different loads while operating with lean burn combustion and reduced thermal load.
3Quantity of substance
If the intake valve closes later in the stroke, then more charge enters the cylinder improving filling, but gas exchange work increases and efficiency decreases
Solution Approach 1:
The intake valve closes early in the intake stroke (before BDC), performing the charging action preliminarily. This early closing reduces the duration of the intake process and the associated pressure losses, decreasing gas exchange work while still achieving sufficient charge quantity through optimized valve timing and port design.
Solution Approach 2:
The early intake valve closing serves multiple functions simultaneously: it limits the charge quantity to control combustion temperature, reduces gas exchange work by shortening the intake process, and works with the lean burn combustion to achieve both efficiency and low thermal load. This multi-functionality resolves the contradiction between charge quantity and gas exchange work.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases engine efficiency, reduces NOx emissions, and lowers pollutant emissions by optimizing charge movement and turbulence, thereby enhancing the compression ratio and knock resistance without the need for costly exhaust treatment systems.
Implementation Method 1
designed as a reciprocating internal combustion engine with at least one squish piston, in particular such that a squish gap height at OT (top dead center) is less than 4 mm
Implementation Method 2
the gas engine is operated according to a Miller cycle process, in particular such that the closing time of the at least one inlet valve of the gas engine is in a crank range of about 50° crank angle before UT (bottom dead center) to about 10° crank angle after UT
Implementation Method 3
the gas engine is operated during the intake stroke with a cylinder charge that has a reduced swirl number according to 'Thien' is less than 2.0
Implementation Method 4
with the gas engine being operated during the intake stroke with a cylinder charge that has a reduced swirl number
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for operating a, in particular stationary, Otto gas engine, wherein the at least one piston (5) of the gas engine (1) designed as a reciprocating internal combustion engine is formed by a squish piston, in particular such that a squish clearance height (hQ) at TDC (top dead center) is less than 4 mm, wherein the gas engine (1) is operated during the intake stroke with a cylinder charge having a reduced swirl number according to "Thien" of less than 2.0, and wherein the gas engine is operated according to a Miller cycle, in particular such that the closing time of the at least one inlet valve (15) of the gas engine (1) lies in a crank angle range of about 50° crank angle before BDC (bottom dead center) to about 10° crank angle after BDC.