Paulius V. Puzinauskas

Laser-Induced Breakdown Spectroscopy for On-Line Engine Equivalence Ratio Measurements

Laser-induced breakdown spectroscopy (LIBS) has been used to measure the equivalence ratio of a spark-ignited engine in a laboratory setting. Spectral features of C (711.3 nm), O (776.6 nm), N (746.3 and 743.8 nm), and CN (broad emission 707–734 nm) were used to quantify the equivalence ratio over a range from Φ = 0.8 to Φ = 1.2. The C/N and C/O peak ratios were found to be successful measurement metrics, compared with a standard exhaust gas oxygen analyzer, for averaged measurements. Some variation in the measurements was observed as a function of engine load. Single-shot data based on a CN/air peak ratio were evaluated using a separate calibration from averaged measurements, and the average of the single-shot data was found to agree well with the exhaust gas oxygen analyzer. The scatter in the single-shot data was substantially higher at lower equivalence ratios. The measurements including the CN peak were slightly sensitive to load, possibly due to pressure changes in the sample as the load increases, or possibly due to changes in the particle size distribution in the gas stream.

Laser-Induced Breakdown Spectroscopy for In-Cylinder Equivalence Ratio Measurements in Laser-Ignited Natural Gas Engines

In this contribution we present the first demonstration of simultaneous use of laser sparks for engine ignition and laser-induced breakdown spectroscopy (LIBS) measurements of in-cylinder equivalence ratios. A 1064 nm neodynium yttrium aluminum garnet (Nd:YAG) laser beam is used with an optical spark plug to ignite a single cylinder natural gas engine. The optical emission from the combustion initiating laser spark is collected through the optical spark plug and cycle-by-cycle spectra are analyzed for Hα (656 nm), O (777 nm), and N (742 nm, 744 nm, and 746 nm) neutral atomic lines. The line area ratios of Hα/O777, Hα/N746, and Hα/Ntot (where Ntot is the sum of areas of the aforementioned N lines) are correlated with equivalence ratios measured by a wide band universal exhaust gas oxygen (UEGO) sensor. Experiments are performed for input laser energy levels of 21 mJ and 26 mJ, compression ratios of 9 and 11, and equivalence ratios between 0.6 and 0.95. The results show a linear correlation (R2 > 0.99) of line intensity ratio with equivalence ratio, thereby suggesting an engine diagnostic method for cylinder resolved equivalence ratio measurements.

Real-time measurement of equivalence ratio using laser-induced breakdown spectroscopy

Abstract This paper demonstrates the use of laser induced breakdown spectroscopy (LIBS) as a diagnostic technique to obtain optical measurements of equivalence ratio in a sparkignited engine. Point measurements were obtained in the exhaust manifold of an automotive engine close to the exhaust port of a cylinder. The experimental apparatus was synchronized with the engine in order to obtain measurements in a fixed position during the cycle. Eighty-shot averaged measurements of equivalence ratio P, obtained in under 10 s, were shown to have ΔP = ±0.05 (95 per cent confidence interval). Single-shot measurements were hindered by noise in the signal, but it is shown that the statistical technique of principal component analysis can significantly improve the precision of the data and allows discrimination between measurements obtained in lean, stoichiometric, and rich conditions. The data presented represent one of the first applications of LIBS to optical measurements of the equivalence ratio in an engine, and considerable improvements are expected with further study.

Ignition and boost effects on large-bore engine in-cylinder heat transfer

Abstract One cylinder of the Colorado State University large-bore test engine was instrumented with fast-response surface thermocouples for heat-transfer analysis. Probes were installed at several locations progressively farther from the ignition source and their outputs were recorded along with combustion pressure using a high-speed data-acquisition system. The engine was operated with two different ignition methods and the manifold boost pressure and cylinder jacket water temperature (JWT) were varied. The recorded surface temperature data were processed to calculate in-cylinder heat transfer. Combustion initiated with a screw-in type pre-combustion chamber resulted in significantly different characteristics than that initiated by a conventional spark plug. The differences in peak heat-flux value could likely be attributed to flame quench distance. Differences in other portions of the cycle could have been caused by significantly increased flame velocities associated with the pre-chamber jet. Increasing boost pressure from 25 to 54 kPa decreased peak heat-flux values about 20–30% and steady-state values about 13%. Increasing JWT 14 K had an insignificant effect on heat flux and combustion pressure.

Temperature and Electron Density Measurements of Laser-Induced Plasmas in Air at Elevated Pressures

ABSTRACT We present time-resolved spectroscopic measurements of 1064-nm Nd:YAG laser-produced plasmas in air at pressures from 0.85 to 48.3 bar. We report temperatures and electron number densities of the plasmas at times between 200 ns and 3 µs after the plasma onset. Neutral atomic oxygen lines at 715 nm and 777 nm are used for temperature measurement through a Boltzmann analysis. Electron number density is measured using Stark broadened atomic hydrogen (Hα) line at 656 nm. We compare experimental results with modeling results obtained from using Taylor-Sedov blast-wave theory coupled with local thermal equilibrium composition calculations.

Movable fiber probe for gas-phase laser-induced breakdown spectroscopy

A movable probe that fiber couples both the beam delivery and the signal collection functions of gas-phase laser-induced breakdown spectroscopy (LIBS) measurements was evaluated. The adjustable probe was used to investigate the effect of delivery fiber curvature on plasma characteristics and the associated effect on LIBS spectra and to further identify issues remaining to facilitate fully fiber-coupled gas-phase LIBS measurements. LIBS data were collected from lean methane-air mixtures of various equivalence ratios and spectroscopically analyzed to establish the ability to determine relative fuel-air ratio. Measurements with straight delivery fiber were compared to those with the fiber curved at specific radii. Decreasing fiber radius of curvature decreased fiber transmission efficiency and reduced the spark formation probability by almost a factor of 2. For constant fiber input energy, this decreased transmission increased the percentage of failed spark formations and influenced the LIBS elemental ratio calculations. However, minimal difference was found between LIBS measurements with straight or curved fiber as long as the output energy and a constant laser beam spot diameter were maintained on the exit beam focusing lens. A significant reduction in data scatter and improved linearity were achieved by using the Balmer series H(alpha) and H(beta) hydrogen emission line ratio as a data selection criterion. Observed linear variation of H/N elemental ratio with equivalence ratio confirmed the possibility of a flexible, light-contained, fully fiber-coupled probe for remote gas-phase LIBS analysis.

A Time Resolved Spectroscopic Study of Laser Generated Plasmas in Air at High Pressures

We present time resolved spectroscopic measurements of 1064 nm laser produced plasma in air at pressures from 0.85 to 48.3 bar. This paper reports on the measurement of temperature and electron number density of the plasmas at times between 100 ns and 3000 ns from the plasma onset. Neutral atomic oxygen lines at 715 nm and 777 nm are used for temperature measurement through a Boltzmann analysis. Electron number density is measured using Stark broadened atomic hydrogen (Hα) line at 656 nm. We employ TaylorSedov blast wave theory to calculate initial plasma pressures and utilize thermo-chemical computations of the plasma to determine plasma compositions. Both ideal and non-ideal behaviors of the plasma are considered. In the former case, plasma composition is computed by minimizing the specific Gibbs free energy and solving the system of nonlinear coupled equilibrium equations. The non-ideal behaviour is taken into account by considering Coulomb interactions between charged particles within the framework of the Debye-Huckel model.

Mass integration of fast-response NO measurements from a two-stroke large-bore natural gas engine

Abstract A thermodynamic two-stroke-cycle engine simulation with a quasi-steady scavenging model was developed and used to mass-integrate cycle-resolved NO measurements made with a fast-response NO analyser. The engine tested was a Cooper-Bessemer GMV-4TF large-bore natural gas engine and the fast NO measurements were made in cylinders 2 and 4 using a Cambustion fNOx400 two-channel fast-response analyser. The engine simulation was deemed to provide a good representation of the cycle-resolved scavenging mass flow. The mass-integrated NO results were compared to Fourier transform infrared (FTIR) steady measurements taken downstream of the cylinders 2 and 4 exhaust-manifold junction. The correlation between the two techniques was linear to within 2 per cent. A strong correlation was exhibited between mass-integrated cycle-to-cycle NO and measured peak and crank angle location of peak combustion pressure. The correlation with peak pressure was slightly better than the location of peak pressure.

Intra-cycle recirculation of partial oxidation products (RePOx): A concept for internal combustion engine combustion control

This work studies the potential for using intra-cycle recirculation of partial oxidation products (RePOx) to control the combustion phasing of advanced internal combustion engine combustion systems such as HCCI. The partial oxidation products are created by extracting a portion of the lean charge products during the expansion stroke and mixing these with the fuel in an auxiliary chamber (RePOx prechamber). The equivalence ratio of the recirculated reactants is controlled by varying the amount of mass extracted. The recirculated partially oxidized products are then reintroduced into the main chamber and mixed with compressed air to facilitate the main chamber reaction. This process was modeled using the CHEMKIN-PRO software package combined with an external program to balance mass and energy for the RePOx system. n-Heptane, modeled with a detailed reaction mechanism, was used as the fuel. The effects of extraction mass, extraction timing, injection timing, prechamber volume and overall equivalence ratio were examined. Varying prechamber volume did not show any effect on the performance or combustion phasing under the conditions and assumptions of this study, whereas injection timing, extraction mass and extraction timing were found to have significant effects on combustion phasing indicating the RePOx concept could possibly be used to control HCCI and derivative internal combustion engine combustion systems. The most significant effect was achieved by varying the extraction mass, where increasing the extraction mass from 5% to 7% advanced the combustion phasing by 8° crank angle. RePOx system was also found to increase the lean limit by 0.05 equivalence ratio compared to conventional HCCI without any specific optimization for lean operation.

Adding a Continuous Improvement Design Element to a Sophomore-Level Thermodynamics Course: Using the Drinking Bird as a Heat Engine

To increase the design experience gained by undergraduate engineering students and to enhance their iterative thinking skills needed in the engineering profession, a new project was developed and assigned in the sophomore-level thermodynamics class taught at the University of Alabama. Students designed a mechanism using a toy drinking bird as a heat engine with the goal of minimizing the time required to raise a small weight a given distance. Besides building teamwork and design skills, several key thermodynamic concepts were also visualized for the students, thus increasing their overall comprehension of the course material.