Bipin Bihari

Development of Advanced Laser Ignition System for Stationary Natural Gas Reciprocating Engines

Laser ignition is considered the prime alternative to conventional coil based ignition for improving efficiency and simultaneously reducing NOx emissions in lean-burn natural gas fired stationary reciprocating engines. In this paper, Argonne’s efforts towards the development of a viable laser ignition system are presented. The relative merits of various implementation strategies for laser based ignition are discussed. Finally, the performance improvements required for some of the components for successful field implementation are listed. Also reported are efforts to determine the relative merit of laser ignition over conventional Capacitance Discharge Ignition (CDI) ignition. Emissions and performance data of a large-bore single cylinder research engine are compared while running with laser ignition and the industry standard CDI system. It was primarily noticed that NOx emissions reduce by 50% under full load conditions with up to 65% reductions noticed under part load conditions. Also, the lean ignition limit was significantly extended and laser ignition improved combustion stability under all operating conditions. Other noticeable differences in combustion characteristics are also presented. Efforts wherein ignition was achieved while transmitting the high-power laser pulses through optical fibers showed performance improvements similar those achieved by using free-space laser ignition.© 2005 ASME

Ignition Characteristics of Methane-Air Mixtures at Elevated Temperatures and Pressures

Lean operation of natural gas fired reciprocating engines has been the preferred mode of operation as it allows low NO x emissions and simultaneous high overall efficiencies. In such engines, the operation point is often close to where the ignition boundary and the knock limiting boundary cross-over. While knocking is, to a large extent, limited by engine design, ignition of lean-mixtures is limited by the mode of ignition. Since significant benefits can be achieved by extending the lean-ignition limits, many groups have been researching alternate ways to achieve ignition reliably. One of the methods, laser ignition, appears promising as it achieves ignition at high pressures and under lean conditions relatively easily. However, most of the current knowledge about laser ignition is based on measurements performed at room temperature. In this paper, ignition studies on methane-air mixtures under in-cylinder conditions are presented. A Rapid Compression Machine (RCM) was designed to reproduce typical in-cylinder conditions of high temperature (∼ 490°C) and pressure (∼ 80 Bar) at the time of ignition. Experiments were performed comparing conventional coil based ignition (CDI) and laser ignition on methane-air mixtures while varying pressure and equivalence ratio systematically. It was observed that substantial gains are likely with the use of laser ignition as it extends the lean-ignition limit to the flammability limit, I.e.,. Φ=0.5. On the other hand, conventional CDI ignition could not ignite mixtures leaner than Φ = 0.6. Also, faster combustion times and shorter ignition delays were observed in the case of laser ignition. Through scans performed for minimum required laser energies (MRE), it was noted that the measured values were substantially higher than those reported elsewhere. However, the trends of these values indicate that a laser ignition system designed for Φ= 0.65 will successfully operate under all equivalence ratios of a typical lean-burn engine.

Performance Analysis of a Natural Gas Generator Using Laser Ignition

A single cylinder spark ignited gasoline engine was modified to operate with natural gas. In such an engine, laser ignition was successfully demonstrated while transmitting the high-power laser pulses via solid core optical fibers. Subsequently, ignition studies were performed while using laser ignition (LI) and conventional spark ignition (SI). However, due to limitations imposed by the engine hardware the adverse conditions for ignition could not be simulated, i.e., of lean operation and high-pressures. As a result, the scope of the study was limited to comparing LI and SI ignition characteristics at various ignition timings. It was observed that both LI and SI resulted in reliable combustion over all ignition timings. Furthermore, LI resulted in higher rates of pressure rise and higher peak cylinder pressures. However, the higher NOx emissions resulting from such conditions might not be representative as the final performance of an engine as it is determined by optimizing ignition timing and other operating parameters.Copyright

Natural Gas Fired Reciprocating Engines for Power Generation: Concerns and Recent Advances

© 2012 Gupta et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Natural Gas Fired Reciprocating Engines for Power Generation: Concerns and Recent Advances

Natural Gas Engine Performance Ignited by a Passively Q-Switched Microlaser

A robust end pumped, passively Q-switched, air-cooled, microlaser was designed and prototyped, and tested in a natural gas fueled single-cylinder engine, and in one cylinder of a turbocharged 6-cylinder engine.

Performance Evaluation of a DENSO developed Micro-Laser Ignition System on a Natural Gas Research Engine

The performance of a prototype micro-laser ignition system developed by DENSO was evaluated on a single cylinder natural gas research engine. Several geometric combinations of pre-chamber spacing and hole sizes were tested at two engine load conditions. Significant improvements in brake thermal efficiency (BTE) were realized due to the extension of the lean ignition limit with a slight penalty in NOx.

In-Cylinder Equivalence Ratio Measurements in an EGR Equipped Engine

A single-cylinder natural gas fueled engine equipped with a Exhaust Gas Recirculation (EGR) system was ignited using a laser. The broadband emission from the spark kernel was spectrally resolved and the peaks corresponding to Hα , N and O atoms were measured for a range of conditions with global equivalence ratios ranging between 0.6 and 1.0, and for Exhaust Gas Recirculation fractions up to 29%. The (Hα /O) and (Hα /N) peak intensity ratios from the spectral scans correlated extremely well (R2 > 0.97) with local oxygen based equivalence ratios. Appropriate relations were developed to relate such values to global equivalence ratios and the EGR rate. For homogenous intake charge, the present LIBS diagnostic enables estimation of one of the two values, global equivalence ratio or EGR rate, with the knowledge of the other.Copyright

In-Cylinder Optical Diagnostics in a Laser Ignited Natural Gas Fired Reciprocating Engine

ABSTRACT In-cylinder combustion gas temperature and rate of heat release are important combustion metrics in internal combustion engines. Such metrics play an important role in the development of strategies for reduced emissions and improved engine performance. The traditional practice has been to measure in-cylinder pressures and deduce the metrics using simple thermodynamic treatments. However, with the availability of improved optics, especially in the field of fiber-optics, optical access to in-cylinder combustion becomes possible. Two diagnostics that measure spectral emission from CO 2 * and OH* species within the combustion environment of a natural gas fueled IC engine were evaluated. The combustion temperatures were varied by operating the engine over an EQR of 0.6 – 1.0 and different levels of exhaust gas recirculation. CO 2 * emission does not lend itself to prediction of crank-angle resolved combustion metrics. However its peak values in a combustion cycle correlated well with both rate of heat release as well as peak combustion temperature during the cycle. In contrast temperatures derived from curve fitting to OH* emission spectra enabled measurement of crank angle resolved in-cylinder temperatures.

In-Cylinder Equivalence Ratio Measurements in a EGR Equipped Engine

A single-cylinder natural gas fueled engine equipped with a Exhaust Gas Recirculation (EGR) system was ignited using a laser. The broadband emission from the spark kernel was spectrally resolved and the peaks corresponding to Hα , N and O atoms were measured for a range of conditions with global equivalence ratios ranging between 0.6 and 1.0, and for Exhaust Gas Recirculation fractions up to 29%. The (Hα /O) and (Hα /N) peak intensity ratios from the spectral scans correlated extremely well (R2 > 0.97) with local oxygen based equivalence ratios. Appropriate relations were developed to relate such values to global equivalence ratios and the EGR rate. For homogenous intake charge, the present LIBS diagnostic enables estimation of one of the two values, global equivalence ratio or EGR rate, with the knowledge of the other.Copyright

NOx Emissions Reduction Using Air Separation Membranes for Different Loads in Gas-Fired Engines

Air Separation Membranes (ASM) could potentially replace Exhaust Gas Recirculation (EGR) technology in engines due to the proven benefits in NOx reduction but without the drawbacks of EGR. Previous investigations of Nitrogen Enriched Air (NEA) combustion using nitrogen bottles showed up to 70% NOx reduction with modest 2% nitrogen enrichment. The investigation in this paper was performed with an ASM capable of delivering at least 3.5% NEA to a single cylinder spark ignited natural gas engine. Low Temperature Combustion (LTC) is one of the pathways to meet the mandatory ultra low NOx emissions levels set by regulatory agencies. In this study, a comparative assessment is made between natural gas combustion in standard air and 2% NEA for different engine loads. Enrichment beyond this level degraded engine performance in terms of power density, Brake Thermal Efficiency (BTE), and unburned hydrocarbon (UHC) emissions for a given equivalence ratio. The ignition timing was optimized to yield maximum brake torque for standard air and NEA. The parasitic loss associated with the usage of ASM technology is presented. It was observed that with 2% NEA, for a similar fuel quantity, the equivalence ratio (Ψ) increases by 0.1 relative to standard air conditions. Analysis showed that lean burn operation along with NEA could pave the pathway for realizing lower NOx emissions with a slight penalty in BTE.Copyright