Image-based plasma morphology determination and LIBS spectra correction in combustion environments

Spectra correction is essential for the quantification of laser-induced breakdown spectroscopy(LIBS) due to the uncertainties in plasma morphology.In this work,we determined the plasma morphology using a charge-coupled device camera and introduced the spectral correction method based on plasma images to a combustion environment.The plasma length,width,volume,and location were extracted from the plasma images.Using a back-scattering setup,the contribution of plasma location fluctuation to the total spectral fluctuation was mitigated.The integral intensity of the plasma image was used as a proxy of the total number density to correct the spectra.Linear relationships were established between the integral intensities of the plasma images and the spectral intensities,under different laser energy levels and gas temperatures.The image-based correction method could significantly reduce the fluctuation of raw spectral intensities when the laser energy was below 240 mJ.Compared with the correction method based on total spectral areas,the proposed method offered significant improvements in the low energy region,which promises to reduce the signal fluctuations in combustion environments while preserving the spatial resolution and mitigating the flow disturbance.

A Stiffness Adjustment Mechanism Based on Negative Work for High-efficient Propulsion of Robotic Fish

The applications of robotic fish require high propulsive efficiency mechanism to prolong the mission time. Though many methods were applied, robotic fish still suffers from low efficiency. To improve the efficiency of robotic fish, this paper proposes a variable stiffness mechanism which is based on the negative work. The live fish adjusts its body stiffness to save energy when the muscles do negative work. Inspired by the live fish, a control mechanism based on negative work is proposed to change the stiffness of the robotic fish for higher efficiency. Changing the stiffness of the robotic fish is to change the joint-stiffness. A fuzzy controller is introduced to mimic the variable stiffness mechanism of the fish and depicts the relationship between the stiffness and the negative work. To evaluate the performance of this controller, a two-joint robotic fish model is established based on its kinematic model and hydrodynamic model. The evaluation results show that the robotic fish reduces the energy consumption and improves the propulsion efficiency when introducing the variable stiffness mechanism. Different environments with the control mechanism impact differently on propulsive efficiency. This mechanism may provide a high efficient propulsion control method for the robotic fish.

Distributed Gas Ignition Using Injection Strategy for High Efficiency and Clean Combustion Under Lean Condition

Jet ignition is an efficient way to achieve lean burn of the engine and a promising strategy to meet the stringent emission regulations in the future.This paper presents a distributed gas ignition(DGI)combustion concept and realizes a DGI combustion mode using a newly designed DGI igniter.The igniter integrates a fuel injector and a spark plug to achieve minimum volume and easy installation.As the mixture preparation within the jet chamber is essential for the performance of the igniter,different jet chamber injection strategies were tested with varying excess air-fuel ratio ranging from 1.4 to 2.0.By addressing the dual injection strategy,the ignition delay and combustion duration were improved evidently.Compared with the single injection strategy,dual injection strategy improves the flexibility when preparing the mixture inside the jet chamber and therefore retains more fuel.The increased energy density of the jet chamber helps to generate more energetic jets under dual injection strategy,resulting in the improvement of ignition and combustion performance with lean burn.A higher thermal efficiency and a leaner limit of the engine are attained with dual injection than that with single injection.Dual injection exhibits its potential in reducing CO and THC emissions to an acceptable level with leaner mixture.Based on dual injection strategy,the maximum indicated thermal efficiency of 45%is achieved.