Direct Injection Fuel Stratification for Cold Start Emissions
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Solution Overview
Problem
Direct injection engines face challenges in reducing raw particulate emissions, especially during the starting phase, due to high fuel overfueling leading to combustion wall wetting and increased emissions, which are exacerbated by frequent cold starts and short journey lengths.
Innovation Solution
The method involves adjusting the fuel release pressure threshold and enrichment factor based on engine conditions, activating the starting device to rotate the crankshaft without initial fuel injection, and injecting fuel only when the pressure exceeds a threshold, with the majority of fuel injection occurring during the compression or expansion phase to minimize fuel reaching the cylinder walls and reduce particulate emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excessive fuel is injected during the starting phase to ensure reliable ignition, then ignition reliability is improved, but raw particulate emissions increase due to combustion wall wetting
Solution Approach 1:
The fuel injection is delayed until the compression phase, after the air has already been compressed in the cylinder. This preliminary compression of air creates a hotter environment that promotes immediate fuel vaporization and combustion upon injection, preventing fuel from contacting and wetting the cooler cylinder walls during the intake and compression phases.
Solution Approach 2:
The injection timing parameter is changed from traditional early injection (during intake or early compression) to late injection (during compression phase close to TDC). This parameter change transforms the thermal environment at the point of fuel introduction, ensuring the fuel encounters hot compressed air rather than cooler walls, thereby promoting vaporization and reducing wall wetting.
2Object-generated harmful factors
If fuel injection is delayed until compression phase to reduce wall wetting, then particulate emissions are reduced, but ignition reliability may be compromised due to shorter preparation time
Solution Approach 1:
The injection timing is optimized to occur during the compression phase at a specific crank angle position that balances two competing requirements: late enough to avoid wall wetting but early enough to allow sufficient mixing and vaporization time. The high compression ratio and resulting high temperature at this stage provide the necessary conditions for reliable ignition even with reduced preparation time.
Solution Approach 2:
The fuel is injected directly into the high-temperature zone near the spark plug and compressed air, creating a localized hot environment that promotes immediate vaporization and combustion. This localized quality change ensures reliable ignition without requiring extensive fuel preparation time.
3Reliability
If high enrichment factor is used during starting phase to ensure combustion, then ignition reliability is improved, but fuel consumption increases
Solution Approach 1:
The enrichment factor is reduced from traditional high values (10 or above) to lower values (1.5 or below) by changing the injection timing to the compression phase. This parameter change leverages the high temperature and pressure conditions during compression to achieve reliable combustion with less fuel, as the hot environment promotes more efficient fuel vaporization and combustion.
Solution Approach 2:
The compressed hot air in the cylinder serves as a self-heating environment that automatically promotes fuel vaporization and combustion without requiring excessive fuel quantities. The thermal energy already present in the compressed air performs part of the work of fuel preparation, reducing the need for high enrichment factors.
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 raw particulate emissions by ensuring efficient fuel evaporation in the combustion chamber, preventing wall wetting, and allowing for a shorter engine start duration while maintaining robust engine performance and reduced emissions.
Implementation Method 1
building up a sufficiently high fuel pressure in the fuel supply system
Implementation Method 2
ensuring the fuel injected, which may be substantially reduced in some cases, evaporates in the combustion chamber
Data Source
AI summary
The methods described allow for reducing particulate emissions from a direction injection engine during a starting phase, while also maintaining the engine start phase within a predetermined threshold. In one particular example, the methods comprise adjusting at least one of a fuel release pressure threshold and enrichment factor based on an engine condition; activating a starting device to rotate a crankshaft coupled to an engine cylinder without injecting any fuel; supplying fuel to the cylinder based on the enrichment factor only when a fuel pressure exceeds the fuel release pressure threshold; and stratifying a cylinder charge while adjusting a fuel injection within a compression phase and/or expansion phase of the engine. In this way, an amount of fuel injected may be evaporated in the combustion chamber while preventing a combustion wall wetting, which allows for reduced particulate emissions, particularly at reduced temperatures.