Two-Stroke Engine Crankcase Fuel Injection for Emission Reduction
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Solution Overview
Problem
Two-stroke gasoline engines face challenges in achieving efficient mixture preparation and reducing hydrocarbon emissions and scavenging losses, particularly during idling and lower partial load ranges, due to insufficient fuel evaporation time and complex design requirements.
Innovation Solution
The method involves using two low-pressure injection nozzles, activated alternately during idling and lower partial load ranges, to inject fuel into the combustion chamber with reduced pulse, ensuring favorable injection conditions and utilizing multi-hole nozzles for improved spray distribution, which avoids piston crown wetting and scavenging losses, while maintaining symmetrical mixture formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If fuel is injected against the piston crown using injectors to enable adequate vaporization, then fuel vaporization is improved, but fuel-wetting of piston and cylinder wall surfaces occurs leading to increased hydrocarbon emissions
Solution Approach 1:
Instead of injecting fuel directly against the hot piston crown for vaporization, the patent inverts the approach by injecting fuel into the crankcase where it mixes with air to form a homogeneous charge. This charge is then compressed and ignited, eliminating fuel-wetting of the piston crown while still achieving complete combustion and reducing hydrocarbon emissions.
Solution Approach 2:
The patent introduces the crankcase as an intermediary chamber where fuel injection occurs. The crankcase serves as a mixing chamber that allows fuel to vaporize and mix with air before entering the combustion chamber, preventing direct contact between fuel and the piston crown while ensuring adequate vaporization through the intermediary mixing process.
2Quantity of substance
If a port in the piston is used to inject fuel into the combustion chamber during idling and lower partial load range, then fuel distribution is achieved, but design complexity, piston strength requirements, and heat dissipation issues increase
Solution Approach 1:
The patent extracts the fuel injection function from the piston structure itself. Instead of creating ports in the piston, the fuel injection system is separated and positioned to inject directly into the crankcase. This removes the complexity, strength requirements, and heat dissipation issues associated with piston ports while maintaining effective fuel distribution through crankcase injection and mixing.
3Speed
If fuel is injected with high impulse into the combustion chamber, then injection speed is improved, but fuel scavenging losses increase during idling and lower partial load range
Solution Approach 1:
The patent applies partial action by injecting only the necessary amount of fuel into the crankcase during idling and lower partial load operation, rather than full injection. The fuel is injected with controlled impulse into the crankcase where it mixes with the incoming air charge, ensuring complete utilization of the fuel without excessive injection that would cause scavenging losses.
4Stability of the object's composition
If the intersection point of nozzle axes is positioned above the piston crown, then mixture preparation is improved, but fuel jets may wet the piston crown causing hydrocarbon emissions
Solution Approach 1:
The patent uses the crankcase as an intermediary mixing chamber where fuel injection occurs. The fuel is injected into the crankcase and mixes with air before the mixture enters the combustion chamber. This intermediary approach ensures proper mixture preparation without the risk of fuel jets directly contacting and wetting the piston crown, thereby preventing hydrocarbon 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 reduces hydrocarbon emissions and scavenging losses, achieving leaner exhaust gas mixtures that enhance hydrogen-carbon conversion with catalytic converters, and allows for even fuel distribution without design complexities, supporting efficient engine operation across load ranges.
Implementation Method 1
the greatest relative velocity due to the opposing velocity components between the fuel flow injected in the direction of the nozzle axis and the air flowing into the combustion chamber from the respective opposite transfer channel can be used for fuel preparation
Implementation Method 2
The injected fuel is carried along by the combustion air flowing into the combustion chamber through the transfer ports and rising from the piston crown, thus distributing itself advantageously within the combustion chamber
Implementation Method 3
This, combined with a catalytic converter, enables efficient hydrogen-carbon conversion due to the increased free oxygen content in the exhaust
Data Source
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AI summary
The invention relates to a method for operating a two-stroke Otto engine comprising at least one cylinder (1) that receives a piston (2); a crankcase (10) which is fluidically connected to the combustion chamber (11) of said cylinder (1) by means of overflow channels (12, 13, 14, 15, 16) on either side of a diameter plane (5) of the cylinder (1) which is determined by the axis of an outlet channel (4); and two fuel injection nozzles (6, 7) that are arranged either side of said diameter plane (5) and whose nozzle axes (8) extend, in the bottom-dead centre position of the piston (2), above the piston base (3) and at least approximately in the outlet flow direction (17, 18) of the overflow channels (12, 14: 13, 15) each provided on the opposite sides of said diameter plane (5), the fuel being injected with reduced momentum into the combustion chamber (11) of the cylinder (1) via only one of the injection nozzles (6, 7) per working cycle when idling and in the lower part-load range.