John Pratapas

A Real-Time Method for Determining the Composition and Heating Value of Opportunity Fuel Blends

Engine manufacturers and researchers in the United States are finding growing interest among customers in the use of opportunity fuels such as syngas from the gasification and pyrolysis of biomass and biogas from anaerobic digestion of biomass. Once adequately cleaned, the most challenging issue in utilizing these opportunity fuels in engines is that their compositions can vary from site to site and with time depending on feedstock and process parameters. At present, there are no identified methods that can measure the composition and heating value in real-time. Key fuel properties of interest to the engine designer/researcher such as heating value, laminar flame speed, stoichiometric air to fuel ratio and Methane Number can then be determined. This paper reports on research aimed at developing a real-time method for determining the composition of a variety of opportunity fuels and blends with natural gas. Interfering signals from multiple measurement sources are processed collectively using multivariate regression methods, such as, the principal components regression and partial least squares regression to predict the composition and energy content of the fuel blends. The accuracy of the method is comparable to gas chromatography.Copyright

Gas Quality Sensor to Improve Biogas-Fueled CHP/DG

Today, renewable fuels such as biogas are being used to fuel combined heat and power (CHP) and distributed generation (DG) systems. The composition of biogas delivered to power generation equipment varies depending upon the origin of the anaerobic digestion process and site-specific factors. For improved process control and optimum utilization of CHP/DG systems, the biogas composition needs to be monitored. A new apparatus has been developed for characterization of hydrocarbon fuel mixtures. The method utilizes near infrared absorption spectroscopy to monitor composition and heating value of landfill gas, natural gas, and other hydrocarbon fuel gases. The measurement is virtually instantaneous. A commercialized version of this sensor is expected to cost less than half the price of gas chromatographs, which are widely used in the gas industry today.Copyright

Experimental Study of a 200 kW Partial Oxidation Gas Turbine (POGT) for Co-Production of Power and Hydrogen-Enriched Fuel Gas

Paper presents the results from development and successful testing of a 200 kW POGT prototype. There are two major design features that distinguish POGT from a conventional gas turbine: a POGT utilizes a partial oxidation reactor (POR) in place of a conventional combustor which leads to a much smaller compressor requirement versus comparably rated conventional gas turbine. From a thermodynamic perspective, the working fluid provided by the POR has higher specific heat than lean combustion products enabling the POGT expander to extract more energy per unit mass of fluid. The POGT exhaust is actually a secondary fuel gas that can be combusted in different bottoming cycles or used as synthesis gas for hydrogen or other chemicals production. Conversion steps for modifying a 200 kW radial turbine to POGT duty are described including: utilization of the existing (unmodified) expander; replacement of the combustor with a POR unit; introduction of steam for cooling of the internal turbine structure; and installation of a bypass air port for bleeding excess air from the compressor discharge because of 45% reduction in combustion air requirements. The engine controls that were re-configured for start-up and operation are reviewed including automation of POGT start-up and loading during light-off at lean condition, transition from lean to rich combustion during acceleration, speed control and stabilization under rich operation. Changes were implemented in microprocessor-based controllers. The fully-integrated POGT unit was installed and operated in a dedicated test cell at GTI equipped with extensive process instrumentation and data acquisition systems. Results from a parametric experimental study of POGT operation for co-production of power and H2-enriched synthesis gas are provided.Copyright

Homogeneous Charge Compression Ignition (HCCI) Engine Fueled With Natural Gas for Stationary Power Generation Applications

In this study, a single-cylinder HCCI engine was used to study the technical feasibility of HCCI engines for stationary power generation applications. The compression ratio (CR) of the engine was set at 13.8:1 considering a hybrid system with diesel micro-pilot injection. The engine was operated under various loads at a rated speed of 1800 rpm. Intake manifold temperature of the air/fuel mixture was used to control the start of combustion (SOC) of the HCCI engine. Oil and coolant temperatures were set at 100°C. Location of peak in-cylinder pressure (PPL) was maintained within 6∼9°ATDC in order to obtain maximum thermal efficiency by initiating the SOC between 2∼4°BTDC. Intake boost was increased up to 2.5 bar absolute to increase engine power output. Results of the HCCI combustion were also compared with those of diesel and diesel micro-pilot natural gas combustion. The results showed that the required intake temperature ranged from 149°C to 261°C depending on engine loads. The highest net mean effective pressure (NMEP) was about 10.6 bar. Higher intake boost pressure would increase NMEP even higher. Maximum indicated thermal efficiency (ITE) was about 49% at the excess air ratio (λ) of 3.2 and maximum combustion efficiency was about 94% at λ = 2.6. Oxides of nitrogen (NOx) emissions were below 10 ppm when λ was above 3. At these excess air ratios, in the good HCCI operating regimes, carbon monoxide (CO), total hydrocarbons (THC), and methane (CH4 ) were equivalent to those of conventional natural gas engines.Copyright

Gas Turbine/Reciprocating Internal Combustion Engine Integrated System for Fuel-Flexible, High Efficiency and Low Emissions Power Generation

This paper reviews the technical approach and reports on the results of ASPEN Plus® modeling of two patented approaches for integrating a gas turbine with reciprocating internal combustion engine for lower emissions and higher efficiency power generation. In one approach, a partial oxidation gas turbine (POGT) is located in the 1st stage, and the H2-rich fuel gas from POGT exhaust is cooled and fed as main fuel to the second stage, ICE. In this case, the ICE operates in lean combustion mode. In the second approach, an ICE operates in partial oxidation mode (POX) in the 1st stage. The exhaust from the POX-ICE (a low BTU fuel gas) is combusted to drive a conventional GT in the 2nd stage of the integrated system. In both versions, use of staged reheat combustion leads to predictions of higher efficiency and lower emissions compared to independently providing the same amount of fuel to separate GT and ICE where both are configured for lean combustion. The POGT and GT analyzed in the integrated systems are based upon building them from commercially available turbocharger components (turbo-compressor and turbo-expander).Modeling results with assumptions predicting 50–52% LHV fuel to power system efficiency and supporting NOx < 9 ppm for gaseous fuels are presented for these GT-ICE integrated systems.Copyright

Integrated Advanced Reciprocating Internal Combustion Engine System for Increased Utilization of Gaseous Opportunity Fuels

The project is addressing barriers to or opportunities for increasing distributed generation (DG)/combined heat and power (CHP) use in industrial applications using renewable/opportunity fuels. This project brings together novel gas quality sensor (GQS) technology with engine management for opportunity fuels such as landfill gas, digester gas and coal bed methane. By providing the capability for near real-time monitoring of the composition of these opportunity fuels, the GQS output can be used to improve the performance, increase efficiency, raise system reliability, and provide improved project economics and reduced emissions for engines used in distributed generation and combined heat and power.

Heating Value Sensor for Producer Gas

Today, producer gas is being utilized as a fuel gas in boilers, internal combustion engines and turbines for heat and power generation. The composition of producer gas varies depending upon the gasification parameters. For improved process control and optimum utilization of these heat and power generating systems, it is desirable to monitor the producer gas composition in real-time. A new method and apparatus has been developed and lab-tested for quantitative characterization of producer gas. Spectroscopic and non-spectroscopic measurements are performed in order to detect both — spectrally active and inactive gases. Both methods are cross-sensitive to more than one gas. The measurements are then processed using multivariate statistical methods — principal components regression and partial least squares to fit a regression model which correlates the experimental measurements to the composition and heating value of producer gas. The fitted regression model is used to estimate the properties of unknown mixtures. The measurements and data processing are done in real time using a high speed hardware control and data acquisition system. A commercialized version of this sensor is expected to cost less than half the price of gas chromatographs, which are widely used in the gas industry today.Copyright

Modeling the Effects of Steam-Fuel Reforming Products on Homogeneous Charge Compression Ignition of n-Heptane

Homogeneous Charge Compression Ignition (HCCI) offers benefits of high efficiency with low emissions, but suffers load range limitations and control issues. A method to improve control of HCCI was numerically investigated based on two separate fuel streams with different autoignition characteristics to regulate timing and heat release at specific operational conditions. In this numerical study n-heptane was selected as the primary fuel, and the secondary fuel was defined as a reformed product of n-heptane (RG). The reformed fuel species composition was experimentally determined based on steam/n-heptane reforming process at a steam/carbon mole ratio of 2:1. In addition to H2 and CO, the reformed fuel stream was composed of CH4 , CO2 , H2 O and non-reformed n-heptane. A single zone model using a detailed chemical kinetic mechanism was implemented on CHEMKIN to study the effects of base fuel and steam-fuel reforming products on the ignition timing and heat release characteristics. The study was performed considering the reformed fuel species composition at total n-heptane conversion (stoichiometric) and also at the composition corresponding to a specific set of operational reforming temperatures. The computational model confirmed that the reformed products have a strong influence on the low temperature heat release (LTHR) region, affecting the onset of the high temperature heat release (HTHR). The ignition timing was proportionally delayed with respect to the baseline fuel case when higher concentrations of reformed gas were used.Copyright

Evaluation of Technical Feasibility of Homogeneous Charge Compression Ignition (HCCI) Engine Fueled with Hydrogen, Natural Gas, and DME

The objective of the proposed project was to confirm the feasibility of using blends of hydrogen and natural gas to improve the performance, efficiency, controllability and emissions of a homogeneous charge compression ignition (HCCI) engine. The project team utilized both engine simulation and laboratory testing to evaluate and optimize how blends of hydrogen and natural gas fuel might improve control of HCCI combustion. GTI utilized a state-of-the art single-cylinder engine test platform for the experimental work in the project. The testing was designed to evaluate the feasibility of extending the limits of HCCI engine performance (i.e., stable combustion, high efficiency and low emissions) on natural gas by using blends of natural gas and hydrogen. Early in the project Ricardo provided technical support to GTI as we applied their engine performance simulation program, WAVE, to our HCCI research engine. Modeling support was later provided by Digital Engines, LLC to use their proprietary model to predict peak pressures and temperatures for varying operating parameters included in the Design of Experiments test plan. Digital Engines also provided testing support for the hydrogen and natural gas blends. Prof. David Foster of University of Wisconsin-Madison participated early in the project by providing technical guidance on HCCI engine test plans and modeling requirements. The main purpose of the testing was to quantify the effects of hydrogen addition to natural gas HCCI. Directly comparing straight natural gas with the hydrogen enhanced test points is difficult due to the complexity of HCCI combustion. With the same air flow rate and lambda, the hydrogen enriched fuel mass flow rate is lower than the straight natural gas mass flow rate. However, the energy flow rate is higher for the hydrogen enriched fuel due to hydrogens significantly greater lower heating value, 120 mJ/kg for hydrogen compared to 45 mJ/kg for natural gas. With these caveats in mind, an analysis of test results indicates that hydrogen enhanced natural gas HCCI (versus neat natural gas HCCI at comparable stoichiometry) had the following characteristics: (1) Substantially lower intake temperature needed for stable HCCI combustion; (2) Inconclusive impact on engine BMEP and power produced; (3) Small reduction in the thermal efficiency of the engine; (4) Moderate reduction in the unburned hydrocarbons in the exhaust; (5) Slight increase in NOx emissions in the exhaust; (6) Slight reduction in CO2 in the exhaust; and (7) Increased knocking at rich stoichiometry. The major accomplishments and findings from the project can be summarized as follows: (1) A model was calibrated for accurately predicting heat release rate and peak pressures for HCCI combustion when operating on hydrogen and natural gas blends. (2) A single cylinder research engine was thoroughly mapped to compare performance and emissions for micro-pilot natural gas compression ignition, and HCCI combustion for neat natural gas versus blends of natural gas and hydrogen. (3) The benefits of using hydrogen to extend, up to a limit, the stable operating window for HCCI combustion of natural gas at higher intake pressures, leaner air to fuel ratios or lower inlet temperatures was documented.