Daniel B. Olsen

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.

Survey of Straight Vegetable Oil Composition Impact on Combustion Properties

The combustion of straight vegetable oil (SVO) in internal combustion engines has shown conflicting results in emissions, power, and engine longevity. Many early studies suggested that SVO should not be considered for long term use in diesel engines. However, waste vegetable oil has been fueling adapted vehicles in progressive communities for years. The issues involved in the combustion of SVO or pure plant oils are complex. Engine injection systems, oil type, lipid acid ratio, and fuel temperature all have significant impact on the engine performance and emissions. A review of published studies of SVO combustion with a focus on known SVO composition and chemical structure reveals trends which merit further study. Future engine tests with known vegetable oil profiles will add significantly to the progression of SVO use in engines.

Development of the tracer gas method for large bore natural gas engines. Part I: Method validation

The tracer gas method is investigated as a means to study scavenging in fuel-injected large-bore two-stroke cycle engines. The investigation is performed on a Cooper-Bessemer GMV-4TF natural gas engine, with a 36-cm bore and a 36-cm stroke. Two important parameters are evaluated from the tracer gas measurements, which are scavenging efficiency and trapped A/F ratio. Measurements with the tracer gas method are compared with in-cylinder sampling techniques to evaluate the accuracy of the method. Two different tracers are evaluated, monomethylamine and nitrous oxide. Monomethylamine is investigated because of its common use historically as a tracer gas. Nitrous oxide is a new tracer gas that overcomes many of the difficulties experienced with monomethylamine. The tracer gas method with nitrous oxide is determined to be accurate for evaluating scavenging efficiency and trapped A/F ratio in comparison to the in-cylinder sampling techniques implemented.

Development of the tracer gas method for large bore natural gas engines. Part II: Measurement of scavenging parameters

In this work the tracer gas method using nitrous oxide as the tracer gas is implemented on a stationary two-stroke cycle, four-cylinder, fuel-injected large-bore natural gas engine. The engine is manufactured by Cooper-Bessemer, model number GMV-4TF. It is representative of the large bore natural gas stationary engine fleet currently in use by the natural gas industry for natural gas compression and power generation. Trapping efficiency measurements are carried out with the tracer gas method at various engine operating conditions, and used to evaluate the scavenging efficiency and trapped A/F ratio. Scavenging efficiency directly affects engine power and trapped A/F ratio has a dramatic impact on pollutant emissions. Engine operating conditions are altered through variations in boost pressure, speed, back pressure, and intake port restriction.

The effect of air-fuel ratio control strategies on nitrogen compound formation in three-way catalysts

Abstract The ability of three-way catalysts (TWCs) to effectively remove CO and NOx from the exhaust is directly controlled by the air-fuel ratio at which the accompanying engine is operated. In a stoichiometric engine, small variations in the air-fuel ratio have large effects on the catalyst performance. These effects include wide variations in removal efficiencies and catalytic production of ammonia. The effect of the air-fuel ratio on catalysts has been well studied on automotive engines; these studies show the importance of maintaining an air-fuel ratio close to stoichiometric conditions. In automotive systems a ‘dithering’ technique is used in which the air-fuel ratio is modulated to widen the window of control. The effect of dithering on industrial engines has not been studied. A research programme was conducted to evaluate the effects of the air-fuel ratio on the performance of three-way catalysts operating on natural gas-fuelled industrial engines, the test programme aims at optimizing the engine based on the performance of the catalyst. This project has shown that dithering is an effective technique for enhancing the performance of TWCs on industrial engines. These results show that the allowable air-fuel ratio deviations are much larger with dithering and that the production of ammonia is significantly reduced.

Formaldehyde Formation in Large Bore Natural Gas Engines Part 1: Formation Mechanisms

Recent testing of exhaust emissions from large bore natural gas engines has indicated that formaldehyde (CH 2 O) is present in amounts that are significant relative to hazardous air pollutant standards. In consequence, a detailed literature review has been carried out at Colorado State University to assess the current state of knowledge about formaldehyde formation mechanisms and evaluate its applicability to gas engines. In this paper the following topics from that review, which bear directly on formaldehyde formation in natural gas engines, are discussed; (1) post combustion equilibrium concentrations; (2) chemical kinetics; (3) flame propagation and structure; (4) partial oxidation possibilities; and (5) potential paths for engine out formaldehyde. Relevant data taken from the literature on equilibrium concentrations and in-flame temperatures and concentrations are presented in graphical form. A map of possible paths for engine out formaldehyde is used to summarize results of the review, and conclusions relative to formation and destruction mechanisms are presented.

Impact of Oxidation Catalysts on Exhaust NO2/NOx Ratio from Lean-Burn Natural Gas Engines

Abstract Oxides of nitrogen (NOx) emitted from internal combustion engines are composed primarily of nitric oxide (NO) and nitrogen dioxide (NO2). Exhaust from most combustion sources contains NOx composed primarily of NO. There are two important scenarios specific to lean-burn natural gas engines in which the NO2/NOx ratio can be significant: (1) when the engine is operated at ultralean conditions and (2) when an oxidation catalyst is used. Large NO2/NOx ratios may result in additional uncertainty in NOx emissions measurements because the most common technique (chemiluminescence) was developed for low NO2/NOx ratios. In this work, scenarios are explored in which the NO2/NOx ratio can be large. Additionally, three NOx measurement approaches are compared for exhaust with various NO2/NOx ratios. The three measurement approaches are chemiluminescence, chemical cell, and Fourier-transform infrared spectroscopy. A portable analyzer with chemical cell technology was found to be the most accurate for measuring exhaust NOx with large NO2/NOx ratios.

Formaldehyde formation in large bore engines. Part 2 : Factors affecting measured CH2O

Current research shows that the only hazardous air pollutant of significance emitted from large bore natural gas engines is formaldehyde (CH 2 O). A literature review on formaldehyde formation is presented focusing on the interpretation of published test data and its applicability to large bore natural gas engines. The relationship of formaldehyde emissions to that of other pollutants is described. Formaldehyde is seen to have a strong correlation to total hydrocarbon (THC) level in the exhaust. It is observed that the ratio of formaldehyde to THC concentration is roughly 1.0-2.5 percent for a very wide range of large bore engines and operating conditions. The impact of engine operating parameters, load, rpm, spark timing, and equivalence ratio, on formaldehyde emissions is also evaluated.

Formaldehyde Characterization Utilizing In-Cylinder Sampling in a Large Bore Natural Gas Engine

This research addresses the growing need to better understand the mechanisms through which engine-out formaldehyde is formed in two-stroke cycle large bore natural gas engines. The investigation is performed using a number of different in-cylinder sampling techniques implemented on a Cooper-Bessemer GMV-4TF four-cylinder two-stroke cycle large bore natural gas engine with a 36-cm (14-in.) bore and a 36-cm (14-in.) stroke. The development and application of various in-cylinder sampling techniques is described. Three different types of valves are utilized, (I) a large sample valve for extracting a significant fraction of the cylinder mass (2) a fast sample valve for crank angle resolution, and (3) check valves. Formaldehyde in-cylinder sampling data are presented that show formaldehyde mole fractions at different times during the engine cycle and at different locations in the engine cylinder. The test results indicate that the latter part of the expansion process is a critical time for engine-out formaldehyde formation. The data show that significant levels of formaldehyde form during piston and end-gas compression. Additionally, formaldehyde is measured during the combustion process at mole fractions five to ten times higher than engine-out formaldehyde mole fractions. Formaldehyde is nearly completely destroyed during the final part of the combustion process. The test results provide insights that advance the current understanding and help direct future work on formaldehyde formation.

Precombustion Chamber NOx Emission Contribution to an Industrial Natural Gas Engine

Abstract This work expands the knowledge base concerning the formation of oxides of nitrogen (NO x ) in the precombustion chamber (PCC) of a four-stroke lean burn (4SLB) industrial gas engine. Two analysis methods were used to characterize specific exhaust constituent concentrations formed in the PCC. The first method extracted gas from the PCC and the overall engine exhaust to be analysed by the industry standard five gas rack (THC, NO x , O 2 , CO 2 , and CO) and a Fourier transform infrared spectrometer (FTIR) to quantify formaldehyde (CH2O), nitric oxide (NO), and nitrogen dioxide (NO2) concentrations. This paper focuses only on NO x . The engine was operated at the manufacturers recommended conditions and at the engines lean limit. A PCC air-fuel ratio (A/F) map was performed at each engine operating condition by varying the fuel supply pressure to the PCC. An analytical model was developed to estimate the mass flow between the PCC and main cylinder, and mass flow out of the PCC through a sample extraction apparatus. The model was applied at specific instances during the engine cycle to clarify raw emissions data obtained directly from a cylindes PCC. The model was developed to determine the origin of the mass sampled from the PCC which, in turn, was used to correct the measured pollutant concentrations. The corrected concentrations allowed for a comparison between NO x , emissions formed in the PCC and the overall engine exhaust on a mass specific basis. PCC-formed NO x , were found to constitute ε10 per cent while operating at the manufactures recommended conditions and upwards of ε75 per cent when at the lean limit. The second test method utilized the high-speed chemiluminescence capabilities of a Cambustion fNOX400 analyser to measure NO concentration in gas extracted from the PCC on a half crank angle basis. The intra-cycle NO data were recorded simultaneously with pressure traces from the PCC and main cylinder by a Hi-Techniques combustion analysis system. The high-speed data acquisition system provided qualitative information on both intra-cycle NO concentrations and cycle-to-cycle variations.