Opportunity to reinvent designs from the ground up
By Doosan Portable Power
Complying with Tier 4 interim (Tier 4i) standards has forced engine and machine manufacturers to make a number of significant design changes to their product offerings, and generator manufacturers have not been immune.
The new standards are part of a national program initiated by the US Environmental Protection Agency (EPA) to reduce emissions from non-road diesel engines through engine controls and reduced-sulfur fuel. The regulations require a 90 percent reduction in diesel particulate matter and a 50 percent reduction in nitrogen oxide (NOx) from Tier 3 regulations. This year marked the beginning of the gradual phase-in to Tier 4 final (Tier 4F) regulations, which are set to take effect from 2013 to 2015, requiring an additional 50 percent reduction in NOx emissions from Tier 4i regulations.
The first set of emission standards, Tier 1, was published in 1996. Since then, diesel engine manufacturers have met Tier 1 and Tier 2 exhaust emissions with in-engine design changes and new technologies. But, because these were all done within the engine, the generator package did not significantly change. There have been design implications with every tier change; the impact of implementing all three prior tier changes combined, however, were less significant than design changes required from Tier 3 to Tier 4F, which have occurred in a shorter time frame.
Tier 3 was the first stage to enforce standards on particulate matter reductions. To account for that, exhaust gas recirculation (EGR) and advanced turbocharging were introduced to make engines cleaner and more fuel efficient without changing overall machine design. Becoming compliant with the next phase of emissions standards, however, will likely require a great deal more activity.
Engine Upgrades-an Overview
Though each engine manufacturer has its own unique design, the following components have been improved or added to engines that use Tier 4i technology.
• Advanced turbocharging was added to vary the speed and volume of airflow into the engine. This helps optimize engine power output and lower emissions.
• A cooled exhaust gas recirculation system was added or improved to reduce NOx emissions.
• A high-pressure common rail fuel system has been improved to allow for more complete and efficient combustion and can ultimately lower particulate matter.
• An exhaust after-treatment system was added to the engine, which includes a diesel oxidation catalyst and diesel particulate filter. The filter traps solid particulate matter and is periodically cleaned via a process called regeneration. This process oxidizes the solid particulate matter and converts it to carbon dioxide to pass through the filter and restore its performance. An exhaust muffler can be added after the after-treatment system to achieve lower noise levels.
• The engine control unit now integrates the engine and exhaust filter control system, which optimizes the overall operation of the machine.
To make the transition to Tier 4 final, it is expected that the after-treatment system will ultimately include a diesel oxidation catalyst and a selective catalytic reduction (SCR) system, augmented with further enhanced electronic controls and an on-board reservoir for diesel exhaust fluid (DEF) storage. DEF is an ammonia-based compound, also known as urea, and is injected into the SCR catalyst to react chemically with the exhaust and further reduce NOx emissions. As with any new technology, the introduction of SCR systems will represent a new learning curve for construction equipment owners and operators as the technology comes to market for certain equipment for the 2014 model year.
Overall, the new Tier 4i engines underwent minor changes from the Tier 3 stage, which didn't result in a dramatic increase in size with the addition of new hardware, either internally and externally. All the additions and improvements have, however, necessitated an additional market expense.
Specific to Generators
Along with the increase in the machines' prices, mobile generator operators also will be well served to become familiar with regeneration indicators. While the regeneration process typically occurs automatically without disruption to operation-either power or productivity-a series of indicator lamps and controls correlate to the engine regeneration process. Training will be an important component to most effectively operating Tier 4i products.
"It was clear very early in our Tier 4i development process that attempting to package this new technology in the existing Tier 3 designs would result in unacceptable product performance compromises," said Todd Howe, manager of global generator products for Doosan Portable Power."
Doosan Portable Power recently released four models-including the G150, G190, G240 and G325-in its Tier 4i mobile generator portfolio.
"Doosan Portable Power has been developing emissions-related product innovations since 1996 with dedicated engineering and design," Howe said. "These new Tier 4i models have been substantially redesigned from their predecessors to incorporate numerous customer-focused innovations in addition to achieving emissions compliance. Without redesigning the package, the machine would have run at an unacceptably higher noise and heat level. Noise reduction and cooling performance are among the most critical customer attributes, and, therefore, were areas of design focus we were not willing to reduce our specifications on. In fact, we chose to improve our performance specifications to add customer value beyond simply providing an emissions-compliant solution."
All features of the new generators are designed to improve the operator experience. Controls are simplified for easy operation, connection panels are made more accessible for improved safety and convenience, and sound levels are reduced between 2 to 5 dBA to ensure quieter operation. Longer runtime, exceeding 24 hours at any load factor, is also achieved with these new generators because of increased on-board fuel capacity. Other Doosan models including the G70, G85 and G125 are currently being finalized to meet the 2012 Tier 4i regulations for respective power ratings, and new G25 and G45 models are under development to meet Tier 4F regulations required in 2013.
Protecting the Environment
"Reducing noise levels and water ingression, as well as increasing fuel efficiency, are top of mind for generator manufacturers in moving toward Tier 4F," Howe said. "Self containment of all fluids inside the package to prevent potential environmental contamination is becoming more of a customer driven and regulatory requirement. The challenge with a self-contained machine, however, is having enough airflow through the package without excessive rainwater intake-which would likely result in a situation that would lead to increased maintenance time for the user to deal with the captured fluid."
To meet the challenge, a compartmentalized approach that involves separating the generator into two compartments can reduce water ingression in all working conditions, while having a positive impact on the cooling system. The powertrain and fuel tank are housed in a self-contained compartment with a small electric-drive cooling fan to move a small volume of air to cool convection heat. The radiator and charge air cooler for the engine is housed in a separate, uncontained compartment.
To allow higher air volumes to be circulated through the radiator and charge air cooler, the radiator compartment utilizes a shaft-driven, radial-style cooling fan. The radial-style fan requires less horsepower from the engine than the traditional blade-style, which can also improve fuel efficiency. Using direct ambient air through the open radiator compartment-vs. warm air that has been moved across the engine-provides better cooling performance against the Tier 4i engine's heat load increase without significantly increasing radiator size. And, it can all be done with only a minor increase to the generator package's footprint.
"The technology being used today in the Tier 4i generators is certainly nothing exotic," Howe said. "The components used are the same as those included in other equipment and are not new to the industry, just new to generators. The engine technology we are using for Tier 4i was introduced in phases to the on-highway truck market in 2002 and 2007, so the technology has been proven and refined. By using familiar components, there's less apprehension when it comes to maintaining the machine."
Predicting the Future
Engine manufacturers are beginning to finalize their Tier 4F engine architecture. It is likely SCR systems will be part of the emissions solution for applications above 75 hp, while sub-75 hp applications will likely see the use of some combination of EGR, diesel oxidation catalyst (DOC) or diesel particulate filter (DPF) aftertreatment and increased electronic controls. Though generator manufacturers have little way of knowing how future emissions standards will affect generator design beyond the Tier 4F stage, there will be assurances for end users.
"Generator packages will be built with the operator in mind and will continue to be reliable, durable and quality high-performance machines," Howe said. "In terms of overall package design, generator manufacturers will need to continue to find space for the new emissions devices and upgraded technology while ensuring the technology does not negatively impact customer attributes."