Negative Valve Overlap Pilot Fuel Injection for HCCI Combustion
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Solution Overview
Problem
In Homogenous Charge Compression Ignition (HCCI) operation of internal combustion engines, low charge temperatures lead to inefficient combustion, increased CO and HC emissions, and potential misfires, which affect engine efficiency and passenger comfort.
Innovation Solution
The method involves controlling intake and exhaust valves to create a negative valve overlap, allowing pilot fuel injection during this overlap to react with residuals, ensuring the right amount of oxygen is present to heat the charge for subsequent main combustion, thereby preventing cooling and improving combustion stability, efficiency, and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excess pilot fuel is injected to ensure sufficient heating of the charge, then combustion stability is improved, but the charge temperature decreases due to cooling effect from un-oxidized fuel
Solution Approach 1:
The control unit determines the amount of pilot fuel based on feedback from sensors measuring oxygen content in residuals and air flow into the cylinder. This closed-loop control ensures the pilot fuel amount is optimized to provide sufficient heating without excessive fuel that would cause cooling, thereby resolving the contradiction between combustion stability and charge temperature.
Solution Approach 2:
The system dynamically adjusts the pilot fuel injection amount as a variable parameter based on operating conditions (air flow, residual oxygen content). By changing this parameter adaptively rather than using a fixed amount, the system achieves sufficient charge heating while preventing the cooling effect that occurs with excess fuel.
2Speed
If pilot fuel injection is performed during negative valve overlap to heat the charge, then combustion timing is improved, but emissions increase if fuel amount is not properly controlled
Solution Approach 1:
The control system uses feedback from oxygen sensors and air flow measurements to precisely control the pilot fuel injection amount. This ensures complete oxidation of pilot fuel, converting potentially harmful unburned hydrocarbons into CO2 and water, thereby maintaining improved combustion timing while reducing emissions.
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 enhances combustion stability and efficiency, reduces emissions, and minimizes the risk of misfires, leading to improved engine performance and passenger comfort by ensuring adequate heating of the combustion charge.
Implementation Method 1
the pilot fuel to react with residuals from a previous combustion... The purpose of the pilot fuel and residual reaction is to heat the charge for the subsequent main combustion
Implementation Method 2
an excess of pilot fuel, providing a rich mixture with the air in the residuals, has a cooling effect on the charge for the subsequent main combustion
Data Source
AI summary
An embodiment of the invention relates to an engine system, and a method in an engine system comprising an internal combustion engine having at least one cylinder (2) at which a piston (3), at least one inlet valve (5), at least one exhaust valve (7), and fuel injection means (11), for injection of fuel directly into the cylinder (2), are provided. The method comprises performing the following steps in at least one of the at least one cylinder: controlling (204) at least one of the at least one intake valve (5) so as to introduce air into the cylinder (2), performing (203, 206) at least one main combustion fuel injection (P21, P22) for a main combustion with air introduced into the cylinder (2), controlling (201), during an exhaust stroke and an intake stroke, the intake and exhaust valves (5, 7) so as to form a negative valve overlap (NVO) to capture main combustion residues, and performing (202) at least one pilot fuel injection (P1) during the negative valve overlap. The amount of fuel in the at least one pilot fuel injection (P1) is at least partly dependent on said introduction of air and at least one of the at least one main combustion fuel injection (P21, P22).