Catalyst Temperature Control Through Multi-Stage Fuel Injection
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Solution Overview
Problem
Existing catalyst temperature increasing systems for diesel engines are inefficient and costly, requiring multiple catalysts in series, where the rear stage catalysts take longer to reach activation temperature due to heat loss in the exhaust gas, necessitating a simpler and more efficient method to heat all catalysts simultaneously.
Innovation Solution
A control unit for a catalyst temperature increasing system that adjusts fuel injection in diesel engines to maintain a theoretical air-fuel ratio across all cylinders, using a single A/F sensor, and employs multi-stage fuel injection patterns to supply unburned hydrocarbons to an oxidation catalyst, which then heats up a downstream selective reduction catalyst efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple catalysts are installed in series to purify different harmful components, then purification performance is improved, but the time required for rear stage catalysts to reach activation temperature increases due to heat loss in exhaust gas
Solution Approach 1:
The system performs preliminary heating of the oxidation catalyst by injecting unburned fuel into it before the selective reduction catalyst can be heated. This preliminary action ensures the oxidation catalyst reaches activation temperature first, and its heat then assists in heating the selective reduction catalyst, solving the time delay problem in multi-catalyst systems
Solution Approach 2:
The oxidation catalyst acts as an intermediary heat transfer medium between the exhaust gas and the selective reduction catalyst. By positioning the oxidation catalyst between the exhaust manifold and the selective reduction catalyst, it captures heat from the exhaust gas and transfers it to the selective reduction catalyst, improving heat distribution efficiency
2Use of energy by moving object
If fuel injection volume is controlled near stoichiometric throughout all cylinders to maintain theoretical air-fuel ratio, then oxidation reaction heat is maximized, but device complexity increases due to requirement for A/F sensor at each exhaust port
Solution Approach 1:
The system extracts and utilizes unburned fuel from the exhaust gas directly at the oxidation catalyst, eliminating the need for precise stoichiometric control in each cylinder. By taking out the unburned fuel component and using it separately for heating the oxidation catalyst, the complex per-cylinder control requirement is removed
Solution Approach 2:
The oxidation catalyst serves multiple functions: it purifies hydrocarbons and carbon monoxide from exhaust gas, and simultaneously acts as a heating element for the selective reduction catalyst. This multi-functionality reduces the need for separate systems and simplifies the overall structure
3Productivity
If front stage catalyst is heated quickly using oxidation reaction heat, then purification of hydrocarbons and carbon monoxide is improved, but rear stage catalyst temperature increase is delayed due to heat loss in exhaust gas
Solution Approach 1:
The system maintains continuous heat transfer from the oxidation catalyst to the selective reduction catalyst through the exhaust gas flow. By ensuring the oxidation catalyst continuously generates heat from unburned fuel and transfers it to the selective reduction catalyst, both catalysts are heated simultaneously and continuously, eliminating the delay in rear stage catalyst heating
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 system achieves rapid and efficient heating of both front and rear stage catalysts with a simpler structure and lower cost by optimizing fuel injection to maximize reaction heat in the oxidation catalyst, thereby reducing the time required for all catalysts to reach activation temperature.
Implementation Method 1
heat is generated by a chemical reaction (oxidation reaction) outside the engine cylinder and on the catalyst itself or near the catalyst
Implementation Method 2
The fuel is then chemically reacted on the catalyst itself or near the catalyst. That is, chemical energy is converted into thermal energy
Implementation Method 3
a catalyst is installed in an exhaust passage, and the catalyst purifies harmful components (HC, CO and NOx) in the exhaust gas
Data Source
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AI summary
A stoichiometric injection volume, which is an amount of fuel to each cylinder(45A to 45D) that is a theoretical air-fuel ratio with respect to an intake air volume into an internal combustion engine (10), is calculated. An allowable amount of hydrocarbons purified by an NSR (61) (first catalyst) is calculated based on a temperature of the NSR (61). It is determined whether warming-up of an SCR (62) (second catalyst) is necessary. If it is determined that the warming-up is necessary, a stoichiometric injection volume is injected in multiple stages such that the hydrocarbons, remaining in the exhaust discharged into an exhaust manifold (12A) in an exhaust stroke of each cylinder (45A to 45D), does not exceed an allowable amount of the NSR (61). Some fuel injected in the post injection is supplied as unburned fuel together with residual oxygen to the NSR (61). An oxidation reaction occurs between the unburned fuel and residual oxygen in the NSR (61) and its reaction heat effectively increases the temperature of the SCR (62).