Pilot Injection Mass Determination for Skip-Fire Combustion Stability
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Solution Overview
Problem
In diesel engines operating in skip-fire mode, skipped cylinders experience progressive drops in compressed gas temperature due to heat losses, leading to longer ignition delays, unstable, and inefficient combustion or misfire, which increases hydrocarbon emissions.
Innovation Solution
A pilot injection mass is injected before the main fuel injection to reduce ignition delay, with the size of the pilot injection mass determined to raise the cylinder temperature for efficient combustion, using equations such as m_fuel,pilot=[m_charge*c_p*(T_desired−T_estimated)]/[LHV_fuel*η_comb] to calculate the required pilot fuel mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If cylinders are skipped in skip-fire mode to reduce engine displacement, then fuel efficiency is improved, but compressed gas temperature drops due to heat losses causing longer ignition delays
Solution Approach 1:
A pilot injection is performed before the main fuel injection to preheat the compressed gas in the cylinder. This preliminary action raises the gas temperature to an acceptable level before the main injection occurs, preventing the temperature drop issue that would otherwise occur during skip-fire operation.
Solution Approach 2:
The system changes the temperature parameter of the compressed gas by introducing a pilot injection. The pilot fuel burns and raises the gas temperature from a sub-acceptable level (caused by heat losses during skipping) to an acceptable level for efficient combustion of the main injection.
2Productivity
If skipped cylinders are re-fired without temperature compensation, then engine displacement is reduced, but ignition delay increases leading to unstable combustion
Solution Approach 1:
Before re-firing a skipped cylinder, a pilot injection is performed to preheat the compressed gas. This preliminary heating action ensures that when the main injection occurs, the gas temperature is sufficient for reliable and stable combustion, preventing ignition delays and combustion instability.
Solution Approach 2:
The pilot injection acts as an intermediary between the skip-fire operation and the main injection. It mediates the temperature issue by heating the compressed gas to an acceptable level, enabling the main injection to proceed with stable combustion despite the previous skipping.
3Reliability
If pilot injection mass is increased to raise gas temperature, then combustion stability improves, but fuel consumption increases
Solution Approach 1:
Instead of using a full main injection to heat the gas, only a partial pilot injection is performed. This pilot injection provides just enough heat to raise the gas temperature to an acceptable level for stable combustion, avoiding the excessive fuel consumption that would result from using a full injection for heating purposes.
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
The pilot injection improves combustion stability by increasing the gas temperature to an acceptable level for the main injection, reducing ignition delays and hydrocarbon emissions, while maintaining or slightly increasing fuel efficiency.
Implementation Method 1
A pilot injection mass is injected before the main fuel injection in order to reduce an ignition delay
Implementation Method 2
the pilot injection improves combustion stability by increasing the gas temperature to an acceptable level for the main injection
Data Source
AI summary
A variety of methods and arrangements are described for determining a pilot injection mass during skip fire operation of an internal combustion engine.