Compression-Ignition Engine Split Injection for Cold Starts
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Solution Overview
Problem
Compression ignition engines, such as diesel engines, face challenges in cold starting due to low ambient temperatures, reduced cranking speed, and ineffective turbochargers, leading to difficulties in generating sufficient power to overcome engine friction and inertia, especially at low engine speeds and high altitudes.
Innovation Solution
A controller in the compression ignition engine splits the main fuel injection into two distinct pulses: a first pulse injected after top dead center to initiate diffusion combustion and a second pulse during the diffusion combustion phase, with the total fuel quantity remaining constant, to enhance power generation and improve cold start performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the fuel quantity injected into the cylinder is increased to generate more power during starting, then the power output increases, but the cylinder temperature decreases due to evaporation, causing poor starting behavior
Solution Approach 1:
The fuel injection is divided into multiple stages: a first fuel injection at a first timing to initiate combustion, and a second fuel injection at a second timing (after TDC) to supplement power. This segmentation allows the combustion process to be staged, ensuring temperature maintenance while achieving sufficient power output.
Solution Approach 2:
A pilot fuel injection is performed before the main fuel injection to pre-heat the combustion chamber and initiate combustion processes. This preliminary action ensures that when the main fuel is injected, the cylinder temperature is sufficient to prevent excessive evaporation and maintain combustion stability.
2Loss of time
If a pilot fuel injection is performed before the main fuel injection, then combustion is initiated earlier, but the in-cylinder temperature decreases due to evaporation, leading to poor starting behavior
Solution Approach 1:
A small pilot fuel injection is performed before the main fuel injection to initiate combustion processes and heat the air-fuel mixture. This preliminary action reduces ignition delay while controlling temperature loss by using a minimal fuel quantity that starts combustion without causing excessive evaporation cooling.
Solution Approach 2:
Instead of injecting the full fuel quantity at once, only a partial amount (pilot fuel) is injected early to start combustion, with the remaining fuel injected later. This partial action approach initiates combustion while minimizing the negative temperature effects of evaporation.
3Use of energy by moving object
If the engine operates on a Miller cycle to reduce in-cylinder volume, then fuel efficiency improves, but the effective compression ratio decreases, resulting in even lower temperatures near top-dead-center
Solution Approach 1:
A pilot fuel injection is performed before the Miller cycle compression to pre-heat the air and initiate combustion processes. This preliminary heating compensates for the lower compression temperatures resulting from the Miller cycle's reduced effective compression ratio.
Solution Approach 2:
The injection timing is optimized for Miller cycle operation, with the second fuel injection timing set after TDC when the piston has started its downward movement. This parameter adjustment ensures that fuel is injected when temperatures are sufficient despite the Miller cycle's lower compression, maintaining combustion stability while preserving fuel efficiency benefits.
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
The split fuel injection strategy reduces ignition delay and increases indicated mean effective pressure, enhancing engine power and improving cold start behavior in various ambient conditions, including low temperatures and altitudes.
Implementation Method 1
ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression
Implementation Method 2
ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression
Implementation Method 3
initiate a diffusion combustion phase in the pressurized combustion chamber
Data Source
AI summary
A compression ignition engine, commercial vehicle comprising such an engine, and a method for improving starting behaviour of such an engine. The engine is operable in a normal mode or a cold start mode. In the normal mode, a fuel injection system is controlled to inject a main fuel injection in a single pulse. In the cold start mode, the main fuel injection is split into a first split main and a second split main. The fuel injection system is controlled to inject the first and second split main in two distinct pulses, wherein the first split main is injected at a delayed timing for initiating a diffusion combustion phase in the pressurized combustion chamber, and wherein the second split main is injected during the diffusion combustion phase into the already combusting air-fuel mix.