Feasibility Considerations: AO Spark-Ignited Engines

Over the past decade, AOs have invested significant capital to retrofit and replace thousands of irrigation pump and other engines reducing emissions by over 80% in this category, and continue to do so as emission limitations and associated compliance deadlines materialize under Rule 4702.  In addition to the high cost-effectiveness and potential technical infeasibility associated with retrofitting or replacing existing AO spark-ignited engines, requiring additional costly controls on existing AO engines is economically challenging and potentially infeasible.

Retrofitting existing spark-ignited engines poses several challenges that are not present when installing new, replacement engines.  The District had to overcome many obstacles and challenges in retrofitting existing AO engines when the District adopted its current emission limit of 90 ppm and has worked closely with AO engine owners and operators and control system manufacturers to ensure compliance with this stringent emission limit.  Efforts to ensure compliance with the current rule limit are continuing today.  Lowering the emission limit from 90 ppmv to 25 ppm or even 11 ppm, results in even greater challenges for existing engines to consistently meet because of the much lower tolerance for being out of compliance. These challenges are outlined in the following list. Details are provided below.

Challenges with retrofitting existing engines:
             1.       Engine power losses from adding controls
             2.       Existing engines may require overhaul
             3.       Existing engines cannot meet lower emissions levels due to narrower margin of compliance
             4.       Control systems must be custom designed
             5.       Errors generated during control system installation
             6.       Retrofit controls can damage an engine
             7.       Engine can damage a control system
             8.       Compliance costs
             9.       Engines operated in remote locations
   
   1. Engine power losses from adding controls
   
   An engine is chosen based on its ability to provide the required power output at a reasonable engine speed (rpm) that will not over-stress the engine over its expected service life.  Add-on emission control systems result in additional loads that the engine may not have been originally designed to accommodate.
   
   In addition, due to the extreme drought conditions, engine owners and operators have needed to increase the power output for well pump engines as the water table has dropped.  As the engines work harder to pump water, there is less power output available to accommodate emission control systems.
   
   2. Existing engines may require overhaul
   
   The engines in use at AOs have been in service for many years, even decades, and are heavily worn.  A worn engine can burn oil, leak fluids, and run rough.
   
   For an uncontrolled engine, some of the effects of engine wear do not have a major effect on the engine's ability to do it's job (e.g. pumping water).  However, the operation of a catalytic emission control system requires that the engine be operated consistently smooth.  An expensive major engine overhaul or rebuild would be necessary to ensure smooth engine operation prior to installing a catalytic emission control system.  Many AOs do not have the resources (e.g., staff, experience, technical training, etc.) to complete an engine overhaul or rebuild without outside assistance.  Meeting more stringent/lower emission standards increases the need for the engine to operate properly.
   
   3. Existing engines cannot meet lower emissions levels due to narrower margin of compliance

   As emission limits are lowered, there is a narrower margin of compliance and proper engine operation becomes more critical.  AOs in the District have to constantly ensure that their engine is properly maintained and within all the appropriate specifications to ensure compliance with the current emission limit, more so than newer engines.  The lower emissions levels will result in additional stresses on the engine and increased maintenance and monitoring efforts that result from operating a retrofitted engine.  Even then, due to the age of the engine and based on engine not appropriately designed for additional add-on systems and the associated loads, engines will not be able to meet the lower limits. 

   4. Control systems must be custom designed
   
   For proper control system design, the engine condition, make, model, power output, and exhaust gas flow rate and temperature must be considered. There are no universal, off-the-shelf, one size-fits-all systems available for purchase. 
   
   Control system design also assumes that an engine is operating properly and smoothly per the engine manufacturer's specifications.  To ensure proper operation of the control system, an engine may need to be overhauled or rebuilt prior to installation of the control system.
   
   A common problem with many retrofit emission control systems is installation of a system on an engine that is not operating smoothly or to engine manufacturer specifications.  Installing a control system on a rough running engine will result in poor control system operation and eventually system and engine damage.  Proper system design and engine operation is more important as emission limits are lowered since the margin of compliance will be much less.
   
   5. Errors generated during control system installation
   
   Site conditions like gas supply pressure can cause an existing engine to operate rough.  If site issues are not addressed prior to installation of a control system, the control system will not operate correctly.
   
   An installer may attempt to correct rough engine operation by making the combustion more fuel rich; however, this technique will not provide lasting results and will cause accelerated engine and control system wear and eventually failure.  An emission control system that is designed to meet lower emission limits will require a larger catalyst element which will be more expensive to replace if permanently damaged.
   
   6. Retrofit controls can damage an engine
   
   For proper control of exhaust pollutants, a catalyst must be operated at a certain temperature range that is higher than normal exhaust temperatures.  Additional fuel is often injected into the engine with the intent that the additional fuel will pass through the combustion chamber and ignite in the exhaust system prior to the catalyst (the high catalyst temperature ignites the fuel).  This extra fuel results in higher engine operating temperatures since some of the extra fuel is combusted during normal engine combustion. The increased engine temperature leads to accelerated engine wear and reduced engine reliability.  Due to wear and older design, increased combustion temperatures lead to engine failure and permanent engine damage.
   
   7. Engine can damage a control system
   
   An existing, worn engine can burn oil and run rough.  Oil in the exhaust stream will foul/mask a catalyst which will result in reduced emission control efficiency and likely permanent damage to a catalyst element.  The air-fuel ratio controller will attempt to adjust engine operation (e.g., injecting more fuel) to keep the control system operating within the specified parameters; however, adjusting engine operation will not correct a fouled catalyst.  Continued operation with a damaged catalyst will lead to permanent catalyst damage.  An emission control system that is designed to meet lower emission limits will require a larger catalyst element which will be more expensive to replace if permanently damaged and this cycle will be repeated further adding to the cost.
   
   8. Compliance costs
   
   Unlike many industries, AOs compete on an international basis and cannot pass increased production costs on to consumers.  AOs must absorb the compliance costs associated with lower emission standards, for example: retrofit and replacement costs; additional maintenance costs; additional monitoring costs; and additional testing costs.
   
   These additional regulatory costs put them at an economic disadvantage to their competitors.
   
   9. Engines operated in remote locations
   
   AO spark-ignited engines are generally located in rural, hard to access areas with minimal oversight since AOs have limited resources and staffing. With seasonal labor and minimal year-round staffing, it is difficult for AOs to provide the frequent and complex maintenance required for retrofitted or new engines equipped with advanced emission controls.  Lower emission limits are achieved only through well maintained engines and control systems.  Lower emissions limits lead to increased maintenance and monitoring efforts.
   
   The oil production industry is the only other major industry in the Valley that has IC engines located in remote locations; however, with the highly technical nature of oil production and refining as compared to agricultural production and additional economic resources, it is feasible for the oil and gas production industry to hire qualified staff dedicated to maintaining and operating IC engines and other equipment on-site.
   
Retrofitting AO engines with emission control systems to meet increasingly stringent emission limits poses unique challenges that are not applicable when installing replacement engines. Based on the challenges outlined above, meeting 25 ppm or even 11 ppm with existing AO engines is not practicable. The additional maintenance, monitoring, and testing, along with the cost of rebuilding engines and the cost of the emission control system, may even be more costly than installing a replacement engine.
