Engine changes to fire trucks in response to new Environmental Protection Agency emissions regulations have been essentially invisible to the end user, a presentation by spokesmen for two leading fire truck makers states.
With regard to power and torque ratings, engine offerings remain similar to those offered before the lower emissions mandated by EPA in 2007, Mark Sackett, chief engineer for Spartan Chassis, reported.
As of 2007, the use of diesel particulate filters on diesel engines has been mandated by the EPA to lower emissions. An ultra-low-sulfur diesel fuel must be used with this device. The new diesel engine standards are expected to reduce smog-causing nitrogen oxide (NOx) emissions nearly 2.6 million tons. Soot or particulate matter (PM) will be reduced by 110,000 tons a year.
With the sulfur content in diesel reduced from 500 parts per million to 15 parts per million, the use of this fuel presents a variety of problems for engine manufacturers.
Sackett and Pierce Manufacturing Director of Research and Development Roger Lackore worked together on a presentation entitled "Impact of 2007 Engine Changes on Fire Apparatus" presented in January at the 20th?annual Apparatus Specification & Vehicle Maintenance Symposium. Sackett focused on power and torque ratings while Lackore's contribution dealt with exhaust aftertreatment.
ENGINE & COOLING SYSTEMS
The combustion-ignition cycle of an engine involves action to a fixed mass of air. A basic four-stroke diesel cycle consists of combustion being replaced by heat addition to the air and exhaust is replaced by a heat rejection process which restores the air to the initial state.
According to Sackett, the 2007 engine changes have increased total heat rejection between five and 30 percent depending on engine make, model and power rating.
"In most cases, the contribution of heat rejection between the radiator and charged air cooler has changed significantly," Sackett said.
This has meant heat exchanger enhancements. The radiator and charge-air-cooler now require different core sizes, new core materials, different fin density and internal turbulation. For example, the series packaging cooling system offered by Spartan utilizes a radiator with a 1,434-inch core area, increased from 1,116 inches. The core material is now copper instead of aluminum. The charge-air cooler has increased from 881 square inches to 941 square inches.
The parallel packaging cooling system offers a radiator with a 900 square inch core area, up from 600 square inches. The charge-air cooler has increased from 300 to 500 square inches.
Air flow enhancements to the fan and shroud include fan size, speed, material, emersion, number of blades and shroud shape. In Spartan's series packaging cooling system, the fan has increased from a 30-inch diameter to 32 inches. The shroud shape is now optimized for fan emersion. Transmission cooler has moved from the bottom tank to a separate shell and tube unit.
The parallel packaging cooling system expands the fan diameter from 28 to 30 inches. Blade depth and shape has also been changed. Transmission cooler is changed from air to oil. All cooling system components are aluminum.
Higher fuel flow rates on certain engines may require changes in supply and return line size and fuel cooler restriction. Regarding air intake, certain engines appear to be more sensitive to air intake temperatures than in the past. Intake locations have been changed and baffles have been added to avoid recirculation.
Under the heading of exhaust aftertreatment, new leak-proof requirements are in place. Leak-proof designs are mandatory to deal with atomized fuel in the exhaust pipe during dosing. Spiral-wrap style flex joints have been replaced with metal bellows to provide a hermetic all-metal pressure barrier and seal that flexes various directions. A heavy duty band clamp known as a Marmon is now used for joints.
Increased engine tunnel heat rejection may be a problem. Under-hood temperatures should not increase significantly, but some components may be closer to the tunnel than before. Items such as turbo charger shields may be required to protect other components.
Since 2007, all diesel engines are required to have diesel particulate filters (DPF) to lower emissions. Engine to DPF insulation is now required by all engine manufacturers. The DPF itself is insulated, and the area behind the DPF may require insulation or shielding to protect body compartments.
Exhaust insulation lowers skin temperature from as high as 700 degrees Fahrenheit to as low as 200 degrees F. As insulation, stainless steel mat and silica quilt mat are the most effective. Header wrap is less effective.
Exhaust gas temperatures can rise to 1,200 degrees F downstream of the DPF. However, NFPA 1901-2009 limits tailpipe gas to 851 degrees F, meaning that exhaust diffusers will be needed. As a result, while bright chrome tailpipes may be offered, do not expect them to stay bright. Most commercial manufacturers are offering only limited warranties on chrome due to discoloration from high temperatures.
Exhaust modifications are mostly frowned upon. Commercial and custom chassis manufacturers will not allow exhaust modifications between the engine and the DPF. Some modifications after the DPF may be permissible. Modifications between the turbo and the DPF could cause serious operational problems and a loss of EPA certification.
Exhaust gas aftertreatment involves a process known as regeneration. With passive regeneration, no fuel is added. Regeneration happens on its own when the temperature is high. With automatic active regeneration, fuel is added to increase DPF temperature. This puts the engine in control. Regeneration happens only if needed. Manual active regeneration occurs while the vehicle is stationary and is initiated by the operator.
DPFs must be cleaned between 50,000 and 150,000 miles of use. The middle section of the unit must be removed to perform cleaning. It also requires special equipment. As of yet, 2007 engines do not have enough miles on them to provide experience yet.
CAB DESIGN CHANGES
Exhaust gas recirculation (EGR) works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. Engines meeting the 2007 emission standards have an enlarged profile for larger or dual turbochargers and additionalEGR piping on the engines. For example, radiator capacity increases by almost 15 percent to compensate for additional demands on the cooling system.
To provide the required engine enclosure clearance, some manufacturers maintain their current cab width and provide pocketed areas or offset engine enclosures to provide the required engine enclosure clearance. Some manufacturers increase cab width to accommodate the wider engine profiles.
Lackore also addressed the issue of increased engine tunnel heat rejection.
"Under-hood temperatures should not increase significantly, but some components may be closer to the tunnel than before," Lackore said. "Multi-layered insulations are available to enhance protection. Thinner or denser insulations are also being utilized."
Ground clearance of vehicles may be reduced dramatically in the area of the DPF. Because a DPF is larger than the 2006 approved muffler, manufacturers may be forced to use blistered or notched compartments. With approximately two inches of clearance for heat shielding and service access, only 28 inches are available for compartments or accessories mounted outboard of the DPF.
Regarding exhaust system packaging, the engine to DPF pipe cannot be modified by a body builder. This ensures EPA compliance. The DPF is primarily a straight exhaust routing installation for most of the larger engines utilized in custom fire chassis. With the limited flexibility of the exhaust system piping, vertical exhausts and specialized installations will have limitations.
The 2007 EPA regulations place limits on four main pollutants for diesel engines.
- Oxides of Nitrogen (NOx) - 1.2 gm/bhp-hr (grams/brake horsepower-hour)
- Non Methane Hydrocarbons (NMHC) - 0.14 gm/bhp-hr
- Carbon Monoxide (CO) - 15.5 gm/bhp-hr
- Particulates - 0.01 gm/bhp-hr
Likewise, OSHA has established indoor air quality limits as per 29CFR?1900.1000.
- Nitric Oxide (NO) - 30 mg/m3(milligram per cubic meter) (eight hour average)
- Nitrogen Dioxide (NO2) - 9 mg/m3?(ceiling)
- Carbon Monoxide (CO) - 55 mg/m3?(eight hour average)
Particulates not otherwise regulated are likewise restricted.
- Total Dust - 15 mg/m3?(eight hour average)
- Respirable Fraction - 5 mg/ m3?(eight hour average)
These limits are based on a fire truck in a sealed garage measuring 14 feet by 14 feet by 50 feet. The truck measures eight feet by nine feet by 40 feet. While idling, the engine consumes 25 hp. Emissions should be 20 percent nitrogen dioxide and 80 percent nitric oxide.
Testing under these conditions indicates the time by which OSHA limits are reached varies by? the substance involved. For nitrous oxide, the limit is reached in 15 minutes. For carbon monoxide, the time limit is 16 minutes, while nitrogen dioxide reaches the limit in 18 minutes. It takes almost four hours before the limit on particulate matter is exceeded.
"Pulling apparatus into a garage bay and shutting down the engine within a minute or two should never exceed the OSHA indoor air quality limits," Lackore said.
Exhaust extraction should be used if operations require vehicle engines to be running while indoors.
Now that 2007 diesel engines are being installed and shipped in fire apparatus chassis, manufacturers are learning more about the impact these engines will have. While the trucks remain almost the same on the exterior, firefighters should be aware of changes under the hood