Progress 09/01/10 to 05/31/15

Outputs
Target Audience:Not relevant to this project. Changes/Problems:We overcame significant technical hurdles with the engine modification and rebuild process. At the completion of the project, the prototype engine functioned very well and met all the objectives that we could test against; however, we were unable to perform longer-duration life testing at a working digester as originally planned because of the setbacks with the engine modifications. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?A conference paper and conference presentation were prepared for the 2015 ASME Internal Combustion Engine Fall Conference in Houston, TX in November. See citation input previously. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1: Develop a biogas-tolerant engine that achieves a recommended oil change interval of more than 100 hours for biogas containing 3000 ppm H2S. The engine oil, oil filter, and piston ring pack were selected to extend the service life of the oil. Experiments showed that minimal acidification, sulfur accumulation, and wear metal accumulation was observed after 100 hours indicating that the oil change interval could be extended beyond that mark. Objective 2: Develop a biogas-tolerant engine capable of a mean-time-between-failure of more than 2000 hours for biogas containing 3000 ppm H2S. A 2000 hour mean-time-between-failure (MTBF) served as the design goal, but a full life test of that duration was not possible. A teardown of the engine was performed after 100 hours of operation with humidified gas containing 3000 ppmv H2S. We observed some oil consumption and deposits on the valves, but no signs of corrosion after this limited durability test. Objective 3: Develop a biogas engine that achieves a 32% brake fuel-conversion efficiency at the rated load and speed. A peak brake fuel-conversion efficiency of 34.2% was observed for the BTEG at the rated load and speed for a synthetic biogas containing 60% (v/v) methane and the balance CO2. In general the observed BTEG efficiency was 1 to 3% higher (additively) than the stock engine. Objective 4: Demonstrate an engine control strategy for time-varying biogas compositions in the range 55 to 80 % methane. The engine control strategy was modified to enable feed-forward control of the spark timing using sensor data from an in-line biogas composition observer. This approach was tested for synthetic biogas mixtures with 60 to 100% (v/v) methane.

Publications

• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2015 Citation: Paul E. Yelvington, John M. Gattoni, Kyle I. Merical, and Andrew L. Carpenter, 2015, A Biogas-Tolerant Engine-Generator for Advanced Agricultural Waste Management, ASME Paper No. ICEF2015-1130.

Progress 09/01/13 to 08/31/14

Outputs
Target Audience: Not relevant to this project. Changes/Problems: Vendor technical hurdles with the engine modification and rebuild process have delayed our progress with the engine modification. We had completed all the engine modifications in September and began performance testing of the prototype system when we observed that the engine could not maintain oil pressure. Upon teardown of the engine we observed severe wear to the crankshaft journal bearings and other internal surfaces. The vendor we had used to apply a corrosion inhibiting coating on the cylinder liners had sandblasted the engine block with an abrasive media. We had observed this sandblast media upon return of the block to us and contacted the vendor about the recommended cleaning process to remove the media before rebuilding the engine. We went above and beyond all recommendations of the vendor; however, some of the sandblasting media had found its way in to the oil gallery of the engine, which led to the eventual failure. We have since procured a second engine long block and repeated the coating process. This time special plugs and block-off plates were fabricated and installed prior to coating. This new prototype engine has since been rebuilt and good oil pressure was observed indicating there are no similar issues on this iteration. A six-month no-cost extension was granted to accomodate for delays caused by these technical hurdles. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? A six-month no-cost extension was granted which will allow dissemination of the results in the next reporting period. What do you plan to do during the next reporting period to accomplish the goals? The remaining work for completion of the Phase II consists of: 1) perform performance testing in our engine laboratory, 2) perform durability testing of the engine and telemetry system, 3) complete patent filing, and 4) disseminate the results.

Impacts
What was accomplished under these goals? Objective 1: Develop a biogas-tolerant engine that achieves a recommended oil change interval of more than 100 hours for biogas containing 3000 ppm H2S Biogas tends to acidify engine oil as sulfur species blow-by the piston rings and enter the crankcase. A prototype strong-base oil filter, which sequesters acids in the oil, was identified as a candidate technology to reach this objective. Several test articles for this new type of oil filter were delivered by the manufacturer. Modifications were made to the engine to allow fitment of the oversized oil filter. In addition, a high Total Base Number (TBN) oil was procured that has reserve alkalinity that delays acidification of the engine oil. Tests with these modifications are forthcoming. This objective will be tested by running the engine using gas containing 3000 ppm H2S and testing the TBN at regular intervals and comparing to the acceptable limit. Objective 2: Develop a biogas-tolerant engine capable of a mean-time-between-failure of more than 2000 hours for biogas containing 3000 ppm H2S Several engine modifications have been implemented to meet this goal. Components were selected based on the results of corrosion testing of representative metal samples in a mixture of oil and sulfuric acid. For example, a Nikasil coating has being applied to the cylinder liner to prevent corrosion. The engine has been outfitted with special low-blowby and corrosion resistant “gapless” stainless steel piston rings, the main and connecting rod bearings of the crankshaft have been replaced with those of Aluminum construction, and the valves and valve seats have been replaced. Several challenges were encountered over the course of the engine modification process, which are discussed elsewhere. These challenges have been overcome and the second-generation engine is running well. This objective will be tested by compression testing the engine at regular intervals and extrapolating to 2000 hours of run time. Objective 3: Develop a biogas engine that achieves a 32% brake fuel-conversion efficiency at the rated load and speed This objective addresses improving the efficiency of the bio-gas engine, whereas the other objectives address improving the corrosion resistance. Custom high-compression pistons were installed in the engine. These pistons will allow the engine to take advantage of the high octane rating of biogas by increasing the compression ratio from 9.7 to 14, while also using gapless piston rings which minimize combustion gas blow-by. The Nikasil coating applied to the cylinder walls reduces frictional losses. The spark timing is also being optimized to improve efficiency as discussed in the next objective. This objective will be tested by determining the brake fuel-conversion efficiency (from measurements of the fuel flow rate, alternator voltage and current, and using the known alternator efficiency) and comparing to the target. Objective 4: Demonstrate an engine control strategy for time-varying biogas compositions in the range 55 to 80 vol. % methane The engine control strategy was modified to allow adjustment of the spark timing based on the methane concentration of the biogas. A method was identified to implement open-loop control of the spark timing based on measured methane concentration. This strategy allows the optimal combustion phasing over a range of biogas compositions to compensate for changes in the quality of the biogas produced by the digester. The methane concentration is being determined using a proprietary algorithm, developed in this project, that does not require any additional specialized sensors. The algorithm was first reduced to practice, and we are filing for patent protection on this invention. This objective will be tested by demonstrating the control of spark timing using real-time biogas methane concentration measurements for several synthetic biogas mixtures.

Publications

Progress 09/01/12 to 08/31/13

Outputs
Target Audience: Not relevant to this project. Changes/Problems: We have experience delays due to several problems with our test instrumentation. For example, we have had repeated mechanical failure and sealing issues with the in-cylinder pressure transducer used to measure the combustion phasing. Also, we have had electrical issues that caused the failure of generator control module. Additionally, we experienced a failure in our lambda (air-fuel ratio) sensor control board. The instrument failures combined to delay the project schedule as the each piece of equipment was repaired. In addition, we have experienced difficulties in maintaining good control over the air-fuel ratio with the widely varying methane concentration in the synthetic biogas (currently CO2/CH4 mix). The stock carburetor is designed for natural gas, which has a significantly different stoichiometric air-fuel ratio compared to low-BTU biogas. We first modified the mechanical carburetor based on recommendations from the manufacturer, but the results were unsatisfactory. We have recently identified an electronic closed-loop fuel pressure regulator that will work with our current carburetor to maintain the correct air-fuel ratio across a wide range of engine load and methane concentrations. This will be implemented within the next month and should resolve this problem. What opportunities for training and professional development has the project provided? Training in entrepreneurship is being offered by our company president as part of our award from EDA’s i6 Green Challenge. How have the results been disseminated to communities of interest? We are seeking patent protection before dissemating results from this project. What do you plan to do during the next reporting period to accomplish the goals? The experimental effort thus far has focused on reducing to practice our strategy/algorithm for determining the methane concentration in biogas using existing engine sensors. That testing is expected to wrap up within the next several weeks. The other engine modifications will then be performed and the engine will be tested in our dynamometer test cell. The initial tests will focus on performance and the later tests will focus on corrosion avoidance. The project will culminate in an extended life test, preferably at a working digester installation.

Impacts
What was accomplished under these goals? Impact Statement: Mainstream Engineering Corporation (MEC) is developing a product to help small/mid-sized dairy and swine farmers turn their manure problems into clean electrical power. How is this done? First, methane-rich biogas is produced by anaerobic digestion of the manure. Anaerobic digestion is a proven technology with 170 digesters operating in the US and many more around the world. The biogas can then be burned in a generator to produce electrical power on the farm. The power can be used to offset consumption or excess power can be sold back to the grid. The problem is that biogas is a sour gas that contains sulfur compounds making it corrosive to standard engine components like bearings, valves, and valve seats. The current solution to this problem is to pretreat the biogas to remove the sulfur, but this pretreatment adds considerable operating costs and maintenance headaches. This maintenance results in increased costs to the farms in terms of consumables and monitoring. In addition, time spent maintaining the system could be better spent on other important activities on the farm. As a result, many small and mid-sized dairies (less than 500 head) don’t even install a generator, opting instead to simply flare the gas without extracting any useful work from it. To address this problem, MEC is developing a biogas-tolerant engine-generator (BTEG) that does not require pretreatment of the biogas. The solution involves a number of differentiating technologies—materials replacement, coatings, engine control strategy changes, and additional sensors. MEC is in the iterative process of making these modifications and testing the outcome. The outcome of this project will be an experimentally tested, first-of-a-kind engine-generator that is tolerant of raw biogas and does not require pretreatment to remove the corrosive impurities. Discussion of Objectives: Objective 1: Develop a biogas-tolerant engine that achieves a recommended oil change interval of more than 100 hours for biogas containing 3000 ppm H2S Biogas tends to acidify engine oil as sulfur species blow-by the piston rings and enter the crankcase. A prototype strong-base oil filter, which sequesters acids in the oil, was identified as a candidate technology to reach this objective. Several test articles for this new type of oil filter were delivered by the manufacturer. Modifications were made to the engine to allow fitment of the oversized oil filter. In addition, a high Total Base Number (TBN) oil was identified that has reserve alkalinity that delays acidification of the engine oil. Tests with these modifications are forthcoming. Objective 2: Develop a biogas-tolerant engine capable of a mean-time-between-failure of more than 2000 hours for biogas containing 3000 ppm H2S Several engine modifications are being implemented to meet this goal. For example, a coating is being applied to the cylinder liner, the engine is being outfit with special low-blowby piston rings, the camshaft/crankshaft bearings are being replaced, and the valves and valve seats are being replaced. All replacement parts have been ordered and these modifications will be made when the current round of engine testing is completed. Objective 3: Develop a biogas engine that achieves a 32% brake fuel-conversion efficiency at the rated load and speed This objective addresses improving the efficiency of the bio-gas engine, whereas the other objectives address improving the corrosion resistance. Custom high-compression pistons were identified and procured. These pistons will allow the engine to take advantage of the high octane rating of biogas. The spark timing is also being optimized to improve efficiency as discussed in the next objective. Objective 4: Demonstrate an engine control strategy for time-varying biogas compositions in the range 55 to 80 % methane The engine control strategy was modified to allow adjustment of the spark timing based on the methane concentration of the biogas. A method was identified to implement open-loop control of the spark timing based on measured methane concentration. This strategy will allow the optimal combustion phasing over a range of biogas compositions to compensate for changes in the quality of the biogas produced by the digester. The methane concentration is being determined using a proprietary algorithm developed in this project. The algorithm was first reduced to practice in this reporting period, and we expect to file for patent protection shortly.

Publications

Progress 09/01/11 to 08/31/12

Outputs
OUTPUTS: The objective of this SBIR program is to develop an engine-generator that is capable of running on raw biogas without clean-up of the gas to remove corrosive hydrogen sulfide gas. The outputs in the second year of this program again involve both technical and commercialization activities. On the technical side, additional instrumentation was added to better characterize the operating characteristics of the spark-ignition, natural gas engine that was selected during the first year of the program. This included a high-speed pressure transducer integrated into a spark plug which is capable of measuring in-cylinder pressures to be used in measuring/controlling combustion phasing. Also, the exhaust manifold was retrofitted with temperature measurements for each cylinder to ensure consistent loading between cylinders when using the biogas fuel. All instruments were fed into a data acquisition system and a robust code was written to read, display, and log all measurement values, perform real-time calculations, and read data being collected from the engine control unit and generator controller. Once all instruments and data acquisition systems were implemented, further engine testing was performed. A surrogate biogas feed system, which was initiated during the last reporting year, was completed. It consists of a methane/carbon dioxide mixture fed into a packed bed humidifier capable of producing a nearly gas stream which is then blended with a metered amount of hydrogen sulfide to produce a synthetic biogas for laboratory testing. In parallel with laboratory testing, a computational model was constructed using commercial engine cycle simulation software. The model is capable of predicting engine power, torque, fuel consumption, knock intensity, emissions and many other characteristics as functions of spark timing and air/fuel ratio. In addition, a programmable engine control unit (ECU) was acquired through collaboration with the manufacturer, which will allow full control and customization of the biogas engine operation. Initial population of controller look-up tables in the ECU has begun using the data and performance maps that were produced by the simulations. Other engine modifications for performance and corrosion resistance are also underway. On the commercialization side, Mainstream participated in the EDA's i6 Green Challenge program and received an additional $100,000 in funding from the USDA to develop a wireless telemetry system for the generator. The telemetry system will allow remote monitoring of the generator, which we feel is key to the third-party owner/operator business model being employed at many new digester installations. PARTICIPANTS: Mainstream Engineering personnel involved in this project include Paul Yelvington (PI) - chemical engineer, Robert Mayo - electrical engineer, Andrew Carpenter - mechanical engineer, and Jerry Wagner - mechanical engineer. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: The Phase II project is on budget, but several months behind schedule due to manpower limitations. Two new mechanical engineers, both experienced with engine development/testing, have been hired to rectify the manpower shortage. The work plan and expected outcomes of this effort remain unchanged.

Impacts
A comprehensive, robust measurement and data acquisition system was completed to fully characterize engine performance for both baseline and surrogate biogas testing. Error analysis was performed to demonstrate the accuracy of Mainstream's proprietary strategy for determining incoming biogas composition. Mainstream has begun programming of an ECU which will allow for optimization of engine-generator performance. Additional funding has been acquired to develop a telemetry monitoring system which will expand the commercial potential of the biogas engine-generator.

Publications

• No publications reported this period

Progress 09/01/10 to 08/31/11

Outputs
OUTPUTS: The objective of this SBIR program is to develop an engine-generator that is capable of running on raw biogas without clean-up of the gas to remove corrosive hydrogen sulfide gas. The outputs in the first year of this program involve our technical and commercialization activities. On the technical side, a spark-ignition, natural gas engine was selected as the test bed for biogas-tolerant engine conversion. The particular engine was selected based on certain features that make it particularly well suited for this application. The engine (which was already packaged for a 25-kW generator application) was procured and installed in our engine test cell. The engine was outfitted with instrumentation to measure the fuel flow rate, air/fuel ratio, and emissions. Additionally, programmers were added to the engine to monitor the state of the engine control unit and generator controller. A switched load bank was constructed that allows applying a prescribed electrical load to the engine. Baseline measurements of engine performance were then performed using methane. A system was designed for preparing synthetic biogas and is now being installed. Modifications to the engine are now underway. An algorithm was developed for determining the composition of the biogas from several simple measurements of engine properties. We expect to file a patent application covering this algorithm. Avoiding acidification of the engine oil is critical to the success of this approach. A specialized oil filter was identified that sequesters acids in the engine oil. Working with a partner company, custom oil filters were designed for this engine, and the engine was also modified to accept to new filters. On the commercialization side, the Larta USDA-CATP program was completed. We are actively pursuing discussions with component suppliers and potential demonstration sites (i.e., dairies with digesters). We have worked with the Florida Department of Agriculture in this regard. As part of the USDA-CATP program, we have crystallized our commercialization strategy and identified potential barriers to commercialization and ways to circumvent them. PARTICIPANTS: Mainstream Engineering personnel involved in this project: Paul Yelvington (PI) - chemical engineer Robert Mayo - electrical engineer Andrew Carpenter - mechanical engineer Jerry Wagner - mechanical engineer TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
An ideal engine platform for our conversion activity was identified. Discussions with the engine supplier indicate a clear pathway for commercialization with Mainstream as an OEM for the biogas-tolerant engine. A new algorithm for simple, real-time determination of the composition of biogas was developed. We expect this outcome to result in a patent filing. A key partnership was formed for the design and supply of custom acid-neutralizing oil filters.

Publications

• No publications reported this period