Multi-mode Internal Combustion Engine with Variable Valve Timing
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Solution Overview
Problem
Internal combustion engines face inefficiencies at low loads due to mechanical friction, heat transfer, and throttling, limiting their ability to operate at high compression ratios without engine knock, which restricts fuel efficiency and power output.
Innovation Solution
The engine operates in two modes: an efficiency mode at low to moderate loads with a lean air-fuel mixture and high compression ratios, and a power mode at higher loads with a richer mixture, using turbulence and controlled ignition timing to prevent knock, while maintaining internal surfaces at lower temperatures to manage auto-ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If compression ratio is increased to improve fuel efficiency at low loads, then fuel economy is improved, but engine knock occurs due to auto-ignition of the air-fuel mixture
Solution Approach 1:
The engine dynamically switches between Otto cycle and Atkinson cycle modes based on operating conditions. The valve timing is adjusted in real-time: in Otto mode (high load), intake valve closes early to enable high compression ratio for power; in Atkinson mode (low load), intake valve closes late to reduce compression ratio and prevent knock, while maintaining expansion ratio for efficiency
Solution Approach 2:
The engine changes the compression ratio parameter dynamically by varying valve timing. At high loads, compression ratio is increased to maximize power output; at low loads, compression ratio is reduced to prevent auto-ignition, while the expansion ratio remains high to maintain thermal efficiency and reduce fuel consumption
2Power
If compression ratio is increased to improve work output per stroke, then power density is improved, but auto-ignition occurs at high temperatures prior to intended ignition
Solution Approach 1:
The engine dynamically adjusts valve timing to control compression ratio based on load conditions. During high-load operation, early intake valve closure creates high compression ratio for maximum power density. During low-load operation, late intake valve closure reduces compression ratio to prevent auto-ignition, ensuring reliable spark-controlled combustion
Solution Approach 2:
The engine performs preliminary cooling of the air-fuel mixture through controlled valve timing. By delaying intake valve closure in Atkinson mode, the mixture is compressed for a shorter duration and at lower temperatures, preventing premature auto-ignition before the intended spark event
3Object-affected harmful factors
If valve timing is adjusted to reduce compression ratio and prevent knock, then engine knock is reduced, but fuel efficiency deteriorates at low loads
Solution Approach 1:
The engine dynamically switches between Otto and Atkinson cycles. In Atkinson mode at low loads, the intake valve closes late to reduce compression ratio and prevent knock, while the expansion stroke remains long to maintain high expansion ratio, ensuring efficient energy extraction and good fuel economy
Solution Approach 2:
The engine independently controls compression ratio and expansion ratio through variable valve timing. In Atkinson mode, compression ratio is reduced to prevent knock while expansion ratio is maintained at high values, allowing the engine to operate at low compression without sacrificing the efficiency benefits of high expansion
4Power
If throttle is used to limit airflow for part-load operation, then power output is controlled, but pumping losses increase due to reduced pressure region
Solution Approach 1:
The engine dynamically adjusts intake valve timing to control airflow instead of using a throttle. By varying the closure timing of the intake valve, the engine controls the amount of air-fuel mixture entering the cylinder, maintaining wide-open throttle conditions and eliminating pumping losses while still achieving part-load operation
Solution Approach 2:
The engine replaces the mechanical throttle system with a valve timing control system. Instead of restricting airflow through a throttle plate that creates pressure drop and pumping losses, the engine uses variable intake valve closure timing to control the effective compression ratio and airflow, eliminating the need for throttling
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 enables a 30% fuel economy savings for vehicles and allows operation at lean mixtures, reducing harmful emissions, thus meeting strict emission norms without complex emissions controls, while maintaining high power density at high loads.
Implementation Method 1
delivering a fluid that includes inlet air to a combustion chamber of an internal combustion engine, the fluid being delivered with an imparted amount of motion that is sufficient to generate at least a threshold amount of turbulence within a combustion volume
Implementation Method 2
internal surfaces within the combustion volume that come into contact with a mixture of the inlet air and a fuel prior to completion of a burn of the mixture are maintained at or below a second target temperature
Implementation Method 3
A high compression ratio in a standard Otto cycle engine generally results in the piston performing a longer expansion in the power stroke, and consequently more work
Implementation Method 4
spark ignition internal combustion engines
Data Source
AI summary
An internal combustion engine is operable in an efficiency mode providing a first power output range between zero and a transition power output and in a power mode providing a second power output range between the transition power output and a maximum power output. The efficiency mode can include a first ignition timing and a first air/fuel ratio of the mixture to avoid premature auto-ignition, and the power mode can include a second ignition timing and a second air/fuel ratio of the mixture to avoid premature auto-ignition of the mixture. To further enable knock free operation of such an engine, turbulence can be imparted to the mixture to promote a faster burn duration and high temperatures that may lead to premature auto-ignition of the mixture can be avoided.