In their own words - Part 1With the 10/02 emissions deadline approaching, a vast amount of misinformation regarding the future of heavy-duty diesel engines still exists. This is the first installment ...
With the 10/02 emissions deadline approaching, a vast amount of misinformation regarding the future of heavy-duty diesel engines still exists. This is the first installment in a series giving engine makers a chance to explain their solution, in their own words…
Volvo is currently the world’s second largest manufacturer of heavy-duty vehicles and the largest manufacturer of heavy-duty diesel engines.
The strength of the research and development assets of the company is derived from a global organization working in concert to achieve innovative technological advancements in the areas of safety research and development, concern for the environment and quality manufacturing processes. That said, the idea of developing a heavy-duty diesel engine capable of performing to the highest performance level of customer expectations while remaining in compliance with EPA02 regulations was a challenge that encompassed all of the core values of Volvo.
As is the case for most heavy-duty diesel engine manufacturers in North America, some form of exhaust gas recirculation (EGR) is the engineering solution that showed the most promise to meet the EPA02 mandate for reducing particulate matter (PM) and oxides of nitrogen (NOx). The purpose for the exhaust gas recirculation is to dilute the fuel air mixture and thus achieve a lower combustion flame temperature to reduce oxides of nitrogen.
In July 2001, Volvo Trucks first announced the technology that would be used in the Volvo 12-liter (D12) diesel engine to meet the Oct. 1, 2002 EPA02 requirement. The EGR system introduced was called V-Pulse (variable pulse) technology. V-Pulse technology, in its most simple form, is a cooled EGR system. The beauty of the system lies in the fact it has the fewest moving parts of the current generation of EGR solutions on the market. Simply stated, Volvo V-Pulse technology uses the engines’ own energy to achieve EGR without the need of a variable geometry turbocharger (VGT).
EGR is achieved by capturing the naturally occurring high-pressure pulses from the exhaust stroke of the combustion cycle. The high-pressure pulses of exhaust gas are captured, cooled, pulsed through a simple reed valve, mixed with fresh intake air and reintroduced to the combustion process. Fuel management is accomplished by flexible fuel injection timing that adjusts and shapes fuel atomization to reduce NOx and PM to an acceptable level.
V-Pulse hardware consists of some basic plumbing, two EGR valves, a two-section cooler, reed valves and a mixing chamber. Volvo’s innovative V-Pulse EGR technology is unique because it does not require a VGT; thus no special maintenance or training will be necessary.
First let’s look at the exhaust side…
Another innovation that makes V-Pulse technology unique is use of two EGR valves. The two modulated EGR valves, located on the exhaust manifold, bleed off up to a maximum of 30 per cent of the exhaust gas for recirculation as the engine speed and load demand. The valves are liquid cooled for efficiency and longevity. The use of two EGR valves allows the exhaust manifold to be divided into two banks. Exhaust pulses from cylinders 1, 2 & 3 are fed through one valve while the pulses of cylinders 4, 5 & 6 are fed through the second. This methodology allows high-pressure pulses of the exhaust strokes to be segregated and captured through the normal engine firing cycle (1-5-3-6-2-4); the system is named V-Pulse for variable pulse technology.
With exhaust gases now divided into two sets of high-pressure pulses, they are sent via their own pressure as the source of energy to the cooling chamber. Inside the cooler, the hot exhaust gases are processed through a small heat exchanger resulting in an average temperature reduction from 650C to approximately 200C.
After being cooled, the gas pulses through a simple reed valve (one way flapper type valve). The valve opens as the pulse pressure reaches the engineered level required to overcome the valves resistance. After the gas passes the valve, the valve shuts instantaneously to prevent gas from flowing back into the cooling chamber. Once the reed valve is closed, pressure begins to build for the subsequent pulse. The cooled exhaust gas continues to the mixing chamber.
Now let’s look at the intake side…
Mixing chamber/fresh air intake
The mixing chamber also has no moving parts. The chamber is a cleverly engineered portion of the normal intake track where the cooled exhaust gas is reintroduced to the intake manifold through simple plumbing. The mixing chamber is designed to create a venturi effect that efficiently mixes the cooled exhaust gas with the fresh air intake from the charge air cooler (CAC) for more complete combustion.
Fuel injection system
The fuel injection of the V-Pulse emission reduction technology is equally important as the variable pulse exhaust. In fact, even the injectors incorporate a type of variable pulse technology to accomplish their task.
Flexible fuel injection timing is used to keep the combustion chamber temperature low enough to reduce NOx and particulate matter to the government prescribed level. Rather than dumping a supply of atomized fuel into the combustion chamber in one pulse, the injector nozzles adjust the spray via flexible timing to control the burn rate thus managing the internal temperature.
Since V-Pulse technology uses the naturally occurring energy of the combustion process to achieve the high pressure necessary to accomplish exhaust gas recirculation, a variable geometry turbocharger (VGT) is not required. Fewer moving parts mean less maintenance. The only moving parts on the V-Pulse EGR system are the two EGR valves and two simple reed valves at the cooling chamber. As previously stated, Volvo does not anticipate any additional maintenance or special service training will be required.
Oil change intervals
The recommended oil change interval for the D12 engine will remain at 25,000 miles without increasing the engine oil capacity. The Volvo D12 engine will require the use of CI-4 rated oil in accordance with VDSIII (Volvo Drain Specification III). CI-4 oil has been specially formulated to contend with the increased soot level resultant in EPA02 diesel engine combustion. Strict adherence to the recommended interval will reduce engine wear and provide better performance.
Heat rejection (the ambient temperature increase under the hood) is a by-product of all EGR systems. Consequently, Volvo increased fan performance to compensate for the additional heat being transferred. The innovative engine-mounted fan shroud ring, introduced in 1984, facilitates excellent cooling performance even under the most arduous conditions when the fan is engaged.
Volvo Trucks has worked diligently to focus the full strength of global technological resources to provide the best possible solution to the EPA02 challenge. In doing so, Volvo has successfully mitigated the impact on the customer as much as possible. No variable geometry turbocharger has been added. No special maintenance or service training is required. Oil drain intervals are unchanged, as is performance.
Unfortunately, the Laws of Thermodynamics seem to dictate that all EPA02 engines will have their fuel economy affected slightly in order to meet the rigorous EPA emission standards. n
– Special to Truck News, this story was prepared by Volvo Trucks North America.
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