Two-Stroke Engine Crossover Channel for Cold Start

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Solution Overview

Problem

Two-stroke engines face difficulties in starting, especially in cold conditions, due to a lean fuel and air mixture caused by fresh air being directed into the scavenger ducts during normal operations, leading to inefficient ignition and the need for multiple attempts to initiate combustion.

Innovation Solution

A scavenging two-stroke internal combustion engine design where a portion of the fuel and air mixture from the carburetor is directly channeled into the scavenger ducts, with a crossover channel and idle start valve allowing a rich mixture to be fed into the combustion chamber during start-up, and fresh air is introduced only after the engine is operational.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If fresh air is directed to the scavenger ducts during normal operations, then fuel efficiency is improved and unspent fuel mixing with combustion gases is reduced, but the fuel and air mixture reaching the combustion chamber during start-up becomes too lean for efficient ignition

Engineering Contradiction:

Improvefuel efficiencyVSAvoidengine start-up

Core Design Contradiction:

Loss of energyVSEase of operation

Solution Approach 1:

The system divides the air intake into separate channels: a first air intake channel for fresh air during normal operation, and a second air intake channel for the fuel and air mixture during start-up. This segmentation allows independent control of air supply paths to resolve the contradiction between fuel efficiency and start-up capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically switches between different operating modes using a choke mechanism and controlled valve operations. During start-up, the choke restricts the first air intake channel while the second channel remains open, allowing rich mixture delivery. After start-up, the choke opens and valve timing ensures fresh air dominates the scavenger ducts, optimizing fuel efficiency.

Inventive Principle:

Principle #15Dynamics

2Object-generated harmful factors

If fresh air enters the combustion chamber first during piston movement, then mixing with combustion gases is reduced, but the initial fuel and air mixture concentration is insufficient for reliable ignition

Engineering Contradiction:

Improveunspent fuel exhaustVSAvoidignition reliability

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The system prepares the combustion chamber with a rich fuel and air mixture through the second air intake channel before the piston reaches positions where fresh air would normally dominate. The choke mechanism pre-restricts the first channel during start-up, ensuring the combustion chamber receives sufficient fuel concentration for reliable ignition before normal operation begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system employs periodic valve operations and choke control to alternately prioritize rich mixture delivery during start-up cycles and fresh air delivery during normal operation cycles. The crankcase pressure variations and valve timing create periodic flow patterns that ensure proper mixture delivery at critical moments while maintaining fuel efficiency during sustained operation.

Inventive Principle:

Principle #19Periodic action

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 design facilitates easier and quicker engine start-ups by creating a richer fuel and air mixture for ignition, improving starting efficiency under both hot and cold conditions while maintaining fuel efficiency and reducing unspent fuel exhaust during regular operations.

Implementation Method 1

The piston defines at least one flow path on its outer circumference that extends radially inward from its outer surface and provides the fluid communication between the fuel and air inlet channel and the combustion chamber

Methodology Applied

Scientific EffectFluid flow through defined passage:

Implementation Method 2

At start of the engine, the air inlet valve is closed

Methodology Applied

Scientific EffectValve closure to control fluid flow: Valve

Implementation Method 3

create a rich mixture into the combustion chamber that is easier to ignite

Methodology Applied

Scientific EffectCombustion: Combustion

Data Source

PatentUS10487721B2Two-stroke internal combustion engine

Publication Date: 2019.11.26 HUSQVARNA AB

AI summary

An internal combustion engine (10), including a cylinder (15) with a cylinder wall (12) defining a combustion chamber (32), a piston (13) reciprocally disposed within the combustion chamber (32) a crankcase (16) including a crankshaft (11) rotatably disposed therein, the piston (13) being connected to the crankshaft (11) by a connecting rod (17), a first scavenger duct (3) extending between the combustion chamber (32) and the crankcase (16), the first scavenger duct (3) including a top port (31a) and a bottom port (31b), a fuel and air inlet channel (22) in fluid communication with the crankcase (16) by way of a piston ported fuel and air inlet port (23) so that the fuel and air inlet channel (22) delivers a fuel and air mixture to the crankcase (16), and an airhead channel (6) in fluid communication with the first scavenger duct (3) by way of a first piston ported air inlet port (7), characterized in that the fuel and air inlet channel (22) is in fluid communication with the airhead channel (6) so that the fuel and air mixture is combinable with the air flow from the airhead channel (6).