The world of diesel-powered RVs is changing, and one of the big reasons is because the Environmental Protection Agency (EPA) keeps updating its rules and regulations, ever tightening the requirements for lower exhaust emissions. Taking a peek into the future (2007 to 2010), emission regulations undergo dramatic changes, with allowable levels of both NOx (nitrogen oxides) and PM (particulate matter — aka soot) being reduced by 90% from 2004 levels. Naturally, this puts manufacturers of diesel engines and exhaust systems under the gun to make technological modifications to meet the new standards.  

Cummins, Inc., maker of powerplants used in many Holiday Rambler coaches, has long been a recognized leader in the field of environmental technology. One of the reasons for this is the corporate philosophy. Cummins looks at the tighter emission rules as an opportunity to step ahead and lead the field of diesel engine manufacturers in emission research and development. And the company is especially well positioned to do this, in part because it has kept the bulk of its emission-related technology in-house where it is easy to control.

One example of Cummins’ approach to real-world research and development is MERLin (Mobile Emissions Research Laboratory), a diesel-powered hybrid truck/RV type vehicle that is dedicated to making on-the-road emission developments in real time during road trips to locations with high altitudes, hot climate, freezing temperatures and mosquito strangling humidity.  

What Cummins is doing to make sure their engines will be able to meet the new standards involves technology that is both inside the engine and outside, in the exhaust system. Internal changes include such things as the development of an advance combustion system. By creating computer simulations of the combustion process, engineers are able to analyze the results of altering fuel delivery parameters and modifying the combustion chamber geometry.

A different approach is lowering the combustion temperature, which in turn reduces NOx, one of the bad actors in the world of air pollution. Combustion temperature reduction is accomplished through the use of cooled exhaust gas recirculation (EGR). But in order to take full advantage of EGR, there must be a high level of precision in the amount of recirculated exhaust gas that is delivered to the combustion chamber, and that requirement has led to the development of an advanced Variable Geometry Turbocharger. It is through the marriage of these various technologies that Cummins powered vehicles will be able to meet the stringent 2007 standards.

Aftertreatment is the term used to describe emissions technology that takes place after combustion — in other words, in the exhaust system. There are technological solutions to both NOx and PM emissions that are engineered into aftertreatment equipment. Some approaches are pretty fascinating — like the “European Heavy Duty Solution” that involves a chemical reductant (liquid urea injected into the exhaust stream) that converts to ammonia in the exhaust and reacts with NOx over a catalyst to form harmless nitrogen gas and water. In this type of system, the catalyst looks similar to a muffler — the liquid urea is carried in a tank — and there must be a precision controlled urea injection system.

The reason the urea system is designed more for places like Europe and not the U.S. is economic. In the U.S., the cost of urea is about equal to the cost of diesel fuel, and fuel efficiency would need to increase by at least 7.5% for there to be an economic break-even. So, for the U.S., there is another technology — NOx Adsorbers. These devices use a combination of base metal oxide and precious metal coatings to control NOx. This system undergoes a form of “regeneration” by periodically operating under conditions in which all excess oxygen is eliminated from the exhaust gas for a brief period of time. This is done by one of two methods — either operating the engine in “rich” mode for a short time, or by injecting raw fuel directly into the exhaust stream ahead of the catalyst. In either event, there must be precise control in order to make everything work properly.  

Yet another method can be used. This one is called a Lean-NOx Catalyst, and it employs unburned hydrocarbons to reduce NOx over a catalyst.

This system requires a continual injection of raw fuel into the exhaust stream ahead of the catalyst.   It’s easy to see that a lot of varied types of research and development are going on in an effort to keep pace with the ever-tightening EPA rules related to NOx. But that’s only part of the challenge. There’s still PM to deal with.  

To meet the new EPA standards related to particulate matter (soot), “active” diesel particulate filters are needed. Exhaust filters made of porous ceramic material capture and trap the soot. You might imagine that the filter will clog up, when enough soot has been trapped — and you would be right in that assumption. So to take care of that problem, the filter system is designed so that after a prescribed amount of soot has accumulated, a high temperature “regeneration event” is triggered that oxidizes the soot and clears the filter. 

The challenge with such an approach to particulate matter reduction is in creating a system that will “regenerate” often enough and under every different type of duty cycle. A fully loaded cargo truck hauling loads over the Rocky Mountains might easily produce high enough exhaust system temperatures to keep the filters clear all the time, but that may not be the case with a flatland RV cruiser who never needs to push the throttle very hard. 

To help us understand more of what is going on in the area of emission controls at Cummins, and what we can expect to see on our diesel powered motorcoaches by the year 2007, we contacted Christine Vujovich, Vice President of Marketing/Environmental Policy at Cummins. Following are some of the questions we asked her, along with her responses.  

Q When it comes to the new emission standards, and the changes in technology that are necessary to keep pace with the more stringent EPA rules, what will be the most visible or most apparent impact on owners of Cummins diesel powered vehicles?

A What the users will see is not dramatically different from what they’re already experiencing. Fuel economy and vehicle performance will be about the same as today. The most significant difference will be the presence of a particulate matter (PM) filter. It will be installed in the exhaust system and will look somewhat like a muffler.  

Q Will owners need to invest more effort, time or money to perform maintenance procedures?

A Much of the maintenance will be the same. For example, oil changes will be at the same intervals. What will change is that there will be a maintenance schedule for the PM filter. The schedule will vary from 150,000 miles to perhaps as high as 400,000 miles, depending upon the vehicle duty cycle. As the particulates load up the filter, the filter will periodically go through a catalytic event to burn them up. What remains is an inert ash, which will accumulate over 150,000 miles or so. This accumulation of ash will require that the filter be removed and replaced, and this can be done at a Cummins Certified dealer. Owners shouldn’t have any trouble finding one of these service places, because there are 3,500 locations nationwide. There will be an indicator to alert the owner when it’s time to have this service work done, but this is not the kind of thing that an owner can do himself.

Also, there will be a crankcase control coalescing filter on 2007 and later engines. This filter addresses the situation that exists as oil-laden blowby gasses escape around the piston and need to be redirected so they don’t get into the atmosphere. The oil removed from the gasses will be routed back into the crankcase. Changing the filter element cartridge is a maintenance operation that will need to be done approximately every 100,000 miles or once per year for average vehicles, and some owners will be comfortable doing it by themselves. Cost of the replacement cartridge is expected to be about $25-30.

Q Will owners need to purchase anything extra to keep the emission systems operational?

A There won’t be additional cost on a day-to-day basis. Once a year, the coalescing filter cartridge will need attention, and at about the 150,000-mile or higher mark, the PM filter will need service. That’s all.

Q What will be the expected impact on vehicle performance and fuel economy?

A Owners will continue to experience the same fuel efficiency and duty ratings as today. One thing that will be important is that owners will need to be sure to use ultra-low sulfur fuel rated at 15ppm in order to allow these emission control systems to work most effectively. 

Q When will all this new technology show up on vehicles?

A Probably late in 2006. In order to take full advantage of the time we have to work on research and development, it will be as close to January 1, 2007 as possible.

The future for diesel-powered RVs is fairly clear — there will be tighter controls for emissions. But the good news is that companies like Cummins are already at work on solutions that will keep many Holiday Rambler owners ahead of the game.