Pre-Chamber Combustion for Lean Mixture Ignition and NOx Reduction
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Solution Overview
Problem
Existing internal combustion engines face challenges in reducing nitrogen oxides (NOx) emissions and efficiently igniting lean fuel-oxidizer mixtures, particularly in spark ignition engines, where high NOx formation and ignition difficulties complicate emissions control and combustion stability.
Innovation Solution
The implementation of a combustion pre-chamber assembly with a controller that admits exhaust gas directly into the pre-chamber, generating energy pulses to increase concentrations of diatomic hydrogen (H2) and carbon monoxide (CO) within the fuel-oxidizer mixture, promoting intermediate species formation and robust ignition while reducing NOx generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spark ignition system is used to ignite lean fuel-oxidizer mixtures, then ignition reliability is improved, but nitrogen oxides emissions increase due to high combustion temperatures
Solution Approach 1:
The combustion chamber is segmented into a pre-chamber and a main chamber. The pre-chamber is dedicated to generating intermediate species (H2, CO) through controlled combustion of rich mixtures, while the main chamber performs the primary combustion function. This segmentation allows the system to achieve reliable ignition through intermediate species transfer while reducing NOx emissions by separating the high-temperature combustion zone from the main combustion process.
Solution Approach 2:
Intermediate combustion species (H2 and CO) serve as mediators between the pre-chamber and main chamber. These species are generated in the pre-chamber through controlled combustion and then transferred to the main chamber to facilitate ignition and combustion of the lean fuel-oxidizer mixture, enabling reliable ignition while maintaining lower combustion temperatures in the main chamber to reduce NOx emissions.
2Object-generated harmful factors
If exhaust gas recirculation is applied to reduce nitrogen oxides, then emissions are improved, but combustion stability deteriorates due to reduced oxygen concentration
Solution Approach 1:
The system segments the combustion process into two distinct zones: the pre-chamber where rich mixture combustion generates intermediate species, and the main chamber where lean mixture combustion occurs with EGR. This allows the EGR system to reduce NOx in the main chamber while the pre-chamber maintains stable combustion through rich mixture control, and intermediate species transfer compensates for the reduced combustion stability in the main chamber.
Solution Approach 2:
The system changes the equivalence ratio parameter between chambers - rich mixture (φ>1) in the pre-chamber and lean mixture (φ<1) in the main chamber. This parameter differentiation allows the pre-chamber to generate sufficient intermediate species to stabilize combustion in the main chamber even under high EGR conditions where oxygen concentration is reduced, thereby maintaining combustion stability while achieving emissions reduction.
3Reliability
If a rich mixture is ignited in the pre-chamber to project flame through the torch nozzle, then ignition of lean mixture in main chamber is achieved, but nitrogen oxides formation increases in the pre-chamber
Solution Approach 1:
The system extracts only the beneficial intermediate combustion species (H2 and CO) from the pre-chamber combustion process through the torch nozzle, while leaving the harmful NOx formation confined to the small pre-chamber volume. The intermediate species are transferred to the main chamber to enable lean mixture ignition, while the limited size of the pre-chamber minimizes overall NOx generation compared to conventional single-chamber designs.
4Quantity of substance
If multiple energy pulses are applied in the pre-chamber, then intermediate species concentration is increased, but energy consumption increases
Solution Approach 1:
The system applies energy pulses periodically to the pre-chamber at optimized intervals and durations. This periodic energy input efficiently generates intermediate combustion species (H2 and CO) by creating controlled combustion events that produce the desired intermediate species concentration. The periodic timing is optimized to maximize intermediate species generation while minimizing total energy consumption, as each pulse is timed to build up the necessary species concentration for main chamber ignition.
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 ignition efficiency, reduces NOx emissions, and extends the useful life of the pre-chamber by generating beneficial intermediate species like H2 and CO, which facilitate complete combustion at lower temperatures, thereby improving engine efficiency and emissions control.
Implementation Method 1
effect a plurality of energy pulses from the energy source within the combustion pre-chamber during one cycle of the piston reciprocating within the bore
Implementation Method 2
The fuel-oxidizer mixture burns inside the variable volume to convert chemical energy in the mixture into heat
Implementation Method 3
The recirculated exhaust gas flow may be mixed with a fresh oxidizer flow to vary an oxygen concentration of the oxidizer mixture entering the combustion chamber
Data Source
AI summary
An internal combustion engine includes a pre-chamber assembly including a wall having an internal surface opposite an external surface, the internal surface of the wall defining a combustion pre-chamber and at least one orifice extending to an aperture through the external surface of the wall; a block having an internal surface defining a bore therein; a piston disposed within the bore and configured for reciprocal translation within the bore, the piston, the bore, and the external surface of the wall at least partly defining a main combustion chamber, and the combustion pre-chamber being in fluid communication with the main combustion chamber via the at least one orifice; an energy source operatively coupled to the combustion pre-chamber; and an exhaust gas recirculation (EGR) valve fluidly coupled to the combustion pre-chamber and an exhaust conduit of the internal combustion engine.