Variable Resolution Cylinder Pressure Sampling for IC Engine Combustion Analysis
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Solution Overview
Problem
Calculating combustion parameters in IC engines based on cylinder pressure measurements is computationally intensive and challenging due to the need for accurate association of pressure measurements with cylinder volume data, particularly requiring high resolution during critical combustion phases.
Innovation Solution
The method involves periodically sampling cylinder pressure at scheduled crank angles with variable resolution, using pre-calculated cylinder volume data from a table, and adjusting crank angles to compensate for misalignment, thereby reducing computational burden while maintaining resolution during critical combustion phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high resolution pressure measurements are taken throughout the entire combustion cycle, then measurement precision is improved, but computational burden increases enormously
Solution Approach 1:
The combustion cycle is divided into multiple crank angle regions (e.g., compression stroke, combustion stroke, expansion stroke), and pressure measurements are taken at different resolutions in each region. Critical regions like combustion receive higher measurement resolution, while less critical regions use lower resolution, thereby reducing overall computational burden while maintaining precision where needed.
Solution Approach 2:
Different measurement resolutions are applied to different portions of the combustion cycle based on their importance. The method uses variable resolution sampling where critical combustion phases are measured at high resolution and other phases at lower resolution, optimizing the balance between measurement precision and computational effort.
2Ease of operation
If pressure measurements are taken at uniform crank angle intervals, then ease of calculation is improved, but measurement precision deteriorates during critical combustion phases
Solution Approach 1:
The measurement interval is made dynamic rather than uniform. The crank angle interval between pressure measurements varies depending on the combustion phase, with smaller intervals during critical combustion events and larger intervals during less critical phases. This dynamic adjustment maintains calculation simplicity while improving precision where needed.
3Device complexity
If crank angle offset compensation is not applied, then device complexity is reduced, but measurement precision deteriorates due to misalignment
Solution Approach 1:
Crank angle offset compensation values are pre-calculated and stored in lookup tables based on engine operating conditions. During real-time combustion analysis, the appropriate offset is retrieved and applied to align pressure measurements with corresponding cylinder volume data, ensuring measurement precision without adding complex real-time calculation requirements.
Data Source
AI summary
Pressure-based combustion parameters of an IC engine are determined based on engine cylinder pressure measurements and crank angle dependent cylinder volume data, where the pressure in a given engine cylinder is periodically sampled at scheduled crank angles to provide a measurement resolution that varies over the combustion cycle for that cylinder, and the cylinder volume data is retrieved from a table of pre-calculated data. The combustion parameter calculations are customized to suit the variable resolution pressure data, and the crank angles used to retrieve the pre-calculated cylinder volume data are offset from the scheduled crank angles to compensate for misalignment of the pressure measurements relative to the scheduled engine crank angles.