Bruce Farrar, communications manager at Cummins, finds the positive points of complying with the EPA. “The rules are being rewritten. No one ever thought emissions would be driving some of the fuel cost savings technology in the industry.”
Since the EPA began to ramp up its enforcement of the Clean Air Act in 2001 requiring all new off-road diesel engines to discharge substantially lower nitrogen oxide, sulfur and carbon monoxide exhaust emissions, engine manufacturers have had their hands full. Their challenge is to design diesel engines that meet the EPA requirements and still deliver the power and fuel efficiency contractors demand. Engineers using control technologies to reduce exhaust emissions are finding the science that makes the engine run cleaner can also make it run more efficiently and economically. Advanced electronic control technology is one of the methods manufacturers are using to keep diesel engine emissions low, vehicle performance high and fuel costs reasonable.
Electronic engine control modules began to appear in gasoline combustion engine vehicles in the late 1980s and have been riding in heavy construction equipment for about 10 years. Systems like MTU Detroit Diesel’s ADEC, Caterpillar’s ACERT technology, Volvo’s V-ACT, Deere’s PowerTech Plus and Mack’s ASET feature electronic engine control modules (ECMs) – small onboard computers – that monitor and adjust the engine’s fuel burn based on data collected from sensors located throughout the machine. ECMs are the engine’s brain.
Today’s ECMs optimize the engine’s combustion efficiency by controlling the fuel injection process, monitoring loads and transmission speeds, managing air intake and exhaust recirculation and controlling aftertreatment systems like diesel particulate filters and diesel oxidation catalysts.
Several equipment manufacturers pair ECMs with machine management control systems that monitor the machine’s health, location, service status and productivity. An example of current control applications in the field is engine idle control. If an operator allows a piece of equipment to idle too long, the machine’s brain has the ability and authority to shut down the engine without the operator’s direction, automatically saving fuel and stopping emissions.
As more robust control technologies migrate down the horsepower band, diesel engine manufacturers are improving the software in ECMs and giving them more authority to make decisions that can increase the engine’s performance and fuel efficiency.
Scott Jenkins, MTU Detroit Diesel’s industrial vehicle manager in North America, sums it up like this: “The company who has the best technologies, brought together in one engine, is the one who will be the leader.”
Higher education for engines
Current engine control technologies tell the engine to adjust after the engine burns its fuel – the ECM reacts to the combustion event instead of controlling the way the fuel burns in the engine. If the ECM knew the variables in each cylinder’s combustion – the exact combustion properties of the fuel blend, how much pressure is required for it to ignite, the EGR temperature – it could match that information with precise performance tables in its memory, and advise the engine to burn the fuel more efficiently.
Dr. Don Stanton, director of advanced engine development with Cummins, and Gregory Shaver, assistant professor of mechanical engineering at Purdue University, are taking evolving engine control technologies to the next level. They are optimistic their research will lead the development of in-cylinder processes that will significantly increase fuel efficiency by controlling the complete combustion event – before, during and after.
Shaver and a select group of students recently installed a 2007 Cummins 6.7-liter B Series diesel engine with fully independent, flexible variable valve actuation at Purdue’s Ray W. Herrick Laboratories. “We are one of maybe three or four research groups worldwide that have a multi-cylinder diesel engine with a fully flexible valve system,” Shaver says. “This allows us to emulate any of the evolving valve actuation systems and puts us in a position to answer a lot of questions.”
A major portion of Shaver’s research involves measuring the pressure inside the engine cylinders during the entire combustion event. Why in-cylinder pressure? Compressing a mixture of diesel fuel and air causes the fuel vapor to auto-ignite as it reaches the right concentration and temperature. Understanding the complete combustion chamber process and how the diesel fuel reacts to pressure will help engineers bring new cost saving technologies to production.
The idea of measuring pressure in engine cylinders isn’t new but until recently, combustion pressure sensors haven’t been tough enough to work in heavy duty in-cylinder applications. That limitation was overcome in May 2002 with the introduction of Kistler Instrument’s ThermoCOMP pressure sensor. Shaver’s lab uses Kistler’s ThermoCOMP 6067C1 water-cooled precision cylinder pressure sensors that withstand the stress of thermodynamic research in small combustion engines.
To measure the pressure of the air inside the cylinder, the team drills a small hole in the engine head and fits the highly sensitive 52.5-mm-long sensor pressure sensor into the opening, letting it extend down to just the top of the cylinder. Powered by the engine’s electrical system, the Kistler sensor measures the pressure inside the cylinder as it works through each combustion event and gives the team data that wasn’t available before heavy-duty pressure sensors were developed. The team will analyze the data using Cummins’ proprietary software and test possible applications on virtual computer engines.
Shaver hopes to use the information his team collects to develop more accurate algorithm tables that will match the engine’s feedback data with exact – not estimated – function control demands. Controlling the fuel burn will mean higher engine fuel efficiency and better engine performance. The lab-quality Kistler sensors cost $2,400 each, but Kistler, as well as other controls manufacturers, are working to produce a sensor with near lab quality accuracy at a production sensor cost. As sensor costs decrease, Shaver hopes they will be put to use in off-road production engines.
In the next year, Shaver’s team will conduct thousands of tests measuring in-cylinder pressure to study several intertwined applications Shaver cites as particularly promising.
Variable valve actuation
Electronic sensors send readings of the engine’s current conditions to the ECM. Based on the feedback the sensor’s signal provides the ECM, the engine’s data is matched to a precise algorithm, sometimes called a lookup table or map-based controller. (The lookup table is a bit of computer memory that stores thousands of predetermined mathematical calculations, or values.) When the sensor sends its signal to the lookup table in the ECM, the table in the control unit finds the closest matching mathematical value associated with that particular sensor signal and sends a command to the appropriate engine component. Shaver gives this example: “When you press the ‘Caps Lock’ key on your computer keyboard, an electrical signal tells your computer to write the next letters in an upper case font.”
Variable valve actuation (VVA) lets the ECM make informed decisions to adjust conditions inside each individual cylinder. “Flexibility in valve motion has been dreamed about for years. Now the sensor technology closed-loop control is catching up with the dream. We will be able to make the most of the fuel injection, exhaust recirculation and turbocharging processes,” Shaver says.
VVA modulates the engine’s compression ratio and gas exchange by allowing the ECM to match the cylinder’s actual pressure data with exact – not predetermined or estimated – response command tables in its memory. Each combustion event can be optimized by controlling the fuel injection timing, air-fuel blend and exhaust recirculation in each separate cylinder. This closed loop technology creates more efficient combustion and squeezes more power out of every drop of diesel, resulting in better fuel economy and less engine wear.
VVA technology should also contribute to smoother engine operations. Diesel engines inject fuel in bursts, not in a constant spray. Timing the fuel injection bursts in each cylinder to occur in a rapid, seamless succession can minimize the staccato pace sometimes found in diesel engines.
Another application that will use the in-cylinder pressure data is Homogeneous Charge Compression Ignition (HCCI). HCCI engines optimize fuel combustion by using some of the homogeneous charge spark ignition (sparkplug) technology used in gasoline engines and the stratified charge compression ignition technology used in diesel engines.
In gasoline and many cooled EGR-based diesel engines, part of the exhaust gas is cooled then re-circulated to combine with fresh air being drawn into the engine. In an HCCI engine, part of the hot exhaust, which contains unspent fuel from the first go round, bypasses the cooling system and is reintroduced immediately back into the air intake process. The reinducted/trapped hot diesel exhaust mixes with the incoming air, raising the air’s temperature and enriching the air/fuel mix with the unspent fuel before the fresh fuel is injected and compression begins.
The challenge in HCCI engines has been that combustion events can happen whenever and wherever the right conditions meet in the cylinder, not necessarily at the top of the piston’s cycle as in a diesel engine. In an HCCI engine, if the air climbs to the right temperature using the heat from the reinducted exhaust, the hot air will cause the diesel fuel to combust early in the cycle without requiring additional compression. The advantage of the HCCI engine is that it reuses fuel that would otherwise have been wasted and sent out the exhaust pipe, but with no controllable combustion initiator like temperature or compression force, managing the HCCI’s fuel burn is difficult and its power is unstable.
One way to control when the combustion event happens is to manipulate the temperature and/or the amount of reinducted exhaust to the cylinder. Using data from the in-cylinder sensors, a VVA system can control the conditions that produce combustion by regulating the amount of hot exhaust gas reinducted into the cylinder. By reopening the air intake valves and adjusting the valve overlap to balance the percentage of cooler air with the hot exhaust gas, it may be possible to control the in-cylinder temperature and time the combustion event, maximizing the engine’s power.
Name that blend
The data in-cylinder sensors provide may also lead to fuel cost savings by teaching the ECM to recognize different biofuels by their combustion properties, then automatically issue commands that will burn that fuel blend most effectively.
Shaver’s team hopes to use data from their in-cylinder pressure sensor research to create software the ECM can use to identify and efficiently burn any biodiesel blend in the machine’s tank, regardless of its feedstock base.
Say a contractor has half a tank of B20 (twenty-percent biodiesel) and needs to fill up but only regular diesel fuel is available. If he tops off his tank with the non-bio fuel, the ECM may be able to match the burn properties of the ‘new’ B20 fuel in its tank with sophisticated lookup tables in its memory and modify the combustion cycle to burn the new blend efficiently – tuning the engine on the fly.
This same sensing technology also has the potential to recognize different feedstocks. Rapeseed, soybean and animal products all have distinct burn properties and those properties affect how the biodiesel blend combusts. Working with Purdue’s agriculture department, Shaver’s group is analyzing how various feedstocks burn and will use that information to develop more matches in the ECM’s lookup tables. Dave Snyder, a grad student studying with Shaver, says, “Different fuel mixes need different estimations. Observing how each fuel burns will help us develop new ECM software.”
As biodiesel fuel blends vary and fuel availability changes, user-friendly engines smart enough to accommodate the majority of fuels will give contractors purchasing flexibility and may be one of the best ways for contractors to budget their fuel costs.
On the horizon
Dr. Xinqun Gui, manager of product engineering for John Deere Power Systems, estimates it will be five to 10 years before VVA and HCCI are viable. Dr. Gui says, “We are open to these new technologies and if we are able to dramatically improve the efficiency of these engines, we could eliminate aftertreatment. There are huge economic cost advantages to this. It’s like the pot of gold at the end of the rainbow.”
Low tech cost saving technologies
Kevin Resch, product manager for John Deere Power Systems, suggests these maintenance and operation tips to maximize your engine’s performance and fuel economy.
- Air Filters: Replace air filters. Clean filters are essential for proper engine operation.
- Injectors: Properly functioning injectors are critical for efficient engine operation.
- Oil: Use proper grade and viscosity oil and change it at the required intervals.
- Fuel: Use the proper blend for the season.
- Tires: Keep tires properly inflated. Replace bias-ply with radials. Replace worn tires to reduce slippage.
- Tools: Keep ground engagement tools sharp and in good working order. Reducing drag and friction from attachments uses less fuel.
- Ballast: Use the proper ballast for conditions. Extra weight burns extra fuel.
- Gear-up/Throttle back: Shift up a gear and bring the throttle back to maintain ground speed.
- Idling: Save fuel by shutting off your engine if you expect to idle more than 10 minutes.
- Size: Match the equipment for the job. Using equipment that is too large or too small uses more fuel.
- GPS/Autosteer: Use your machine’s electronic position system. Eliminating overlap can reduce fuel consumption.