Turbocharger Wastegate Oscillation for Cold Start Emissions
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Solution Overview
Problem
Cold engine starting results in higher hydrocarbon emissions due to incomplete combustion and low catalyst conversion efficiency, as the engine and catalyst are relatively cold, leading to increased hydrocarbon emissions during this period.
Innovation Solution
Oscillating the position of a turbocharger wastegate between two open positions to increase turbulence in the exhaust system, enhancing the mixing of oxygen and hydrocarbons within the turbocharger housing and exhaust passages, thereby improving hydrocarbon oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the engine is cold started, then the engine can be prepared for service, but hydrocarbon emissions increase due to incomplete combustion and low catalyst conversion efficiency
Solution Approach 1:
The wastegate is oscillated between fully open and fully closed positions to create mechanical vibrations in the exhaust flow. This oscillation generates turbulence that enhances mixing of oxygen and hydrocarbons in the exhaust system, promoting hydrocarbon oxidation before the catalyst reaches operating temperature.
Solution Approach 2:
The wastegate undergoes periodic oscillation during cold start conditions, alternating between fully open and fully closed positions. This periodic action creates recurring turbulence pulses in the exhaust flow, continuously enhancing hydrocarbon mixing and oxidation throughout the cold start period until the catalyst becomes effective.
2Ease of operation
If the catalyst is cold, then the engine can be started, but conversion efficiency of the catalyst is low
Solution Approach 1:
The wastegate oscillation creates turbulence and enhances hydrocarbon oxidation in the exhaust system before the catalyst reaches its light-off temperature. This preliminary oxidation action reduces the burden on the cold catalyst and begins converting hydrocarbons earlier in the cold start process.
3Object-generated harmful factors
If the wastegate position is oscillated, then turbulence and mixing of exhaust gases increase, but this may affect engine power and drivability
Solution Approach 1:
The wastegate transitions from a static position to a dynamic oscillating position during cold start conditions. This dynamic operation allows the system to adapt to cold start requirements by creating necessary turbulence for hydrocarbon oxidation, while the oscillation is controlled to cease once the catalyst reaches operating temperature, thereby preserving engine power and drivability during normal operation.
Solution Approach 2:
The wastegate oscillation is implemented as a temporary periodic action only during cold start conditions. By limiting the oscillation to this specific operational window and discontinuing it when the catalyst becomes effective, the system achieves hydrocarbon reduction when needed without compromising engine power and drivability during sustained operation.
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 engine hydrocarbon emissions during cold starts without compromising engine power or drivability, and can be adjusted for various operating conditions to optimize emissions reduction.
Implementation Method 1
turbulence of exhaust gas flow within the turbocharger and upstream of the turbocharger may be increased by oscillating the position of the turbocharger wastegate
Implementation Method 2
hydrocarbons may be oxidized within a turbocharger housing and nearby exhaust passages
Data Source
AI summary
A method for operating an engine that includes a turbocharger with a wastegate is described. In one example, the method includes oscillating a position of the wastegate during cold engine starting as a function of a speed of an engine. The wastegate position may be adjusted to follow a square wave, sinusoidal wave, or triangle wave.