Improving Diesel Technology

Improving Diesel Technology

There is a “shade tree” law from the 1970s that states that computing capacity doubles every few years. In fact, computing capacity for the size of the computer or device has outstripped that by several orders of magnitude in the last five years. As evidence of that, we now see cell phones that were only found in science fiction or spy novels not so long ago, and iPods and personal audio players that put 10,000 recordings in the palm of a 14-year-old’s hand. This technology explosion has profoundly impacted the engine and motive power industry from top to bottom; from lawn mowers to 500-ton GCW mine trucks. Just in time as well, since the EPA and its equivalents in most of the industrialized world have adopted ever more stringent emissions requirements that would be absolutely impossible to meet without computer controls of engine operation and performance.

Another aspect of this merger of mechanical and electronic technologies is the convergence of diesel and gasoline engine management technologies so that in the more advanced versions of each type of engine, just about the only things different are the compression ratios, rpms and the strength of the working parts.

Finally, the most important part of this revolution is the restriction of information that is starting to strangle the non-OEM world, which is likely to continue in the future. Simply put, if a computer is going to be used to control and monitor critical functions in a power unit, it is still a computer, and acts and works like a computer. This means no moving parts and virtually no opportunity to reverse-engineer what is in the brain that measures and controls the engine.

To see how this works, the first thing that we have to understand is what differences, if any, there are between advanced 2005 gas and diesel engines. Consider the following:

  • Both gas and diesel engines inject fuel directly into the cylinders using electronically controlled common rail injection systems with one injector per cylinder. (Honda now has a gas engine that only uses a spark plug for starting, with “compression ignition” thereafter);

  • Both gas and diesel engines can be made without any throttles or upstream air flow controls;

  • All fuel quantity, quality and timing of injection are controlled by computer means with no mechanical intervention;

  • Any performance enhancements like supercharging, turbocharging or both are computer-controlled;

  • Valve timing and lift are electronically controlled; and

  • Any emissions-related combustion enhancements like excess air, exhaust gas recirculation, lean burn or similar strategies are computer-controlled.

Much of this advancement is coming from Bosch in Germany, where the emissions standards are, in some cases, stricter than in the United States. For example, Figure 1 illustrates the gas fuel supply for a common rail system and Figures 2  and Figure 3 depict common rail diesel systems. Both examples are pressurized by mechanical or electric pumps that are not “tied” to the engine for the purposes of injection timing or otherwise.

In addition, there are few diesels or gas engines in vehicles that are not “drive by wire” with the “gas pedal” attached to the computer and a throttle body or other air regulation system completely controlled by the computer responsible for engine speed regulation. This system can take several forms:

  1. In a diesel, there is no air flow control, all speed and power controls are through the fuel injection, turbo boost pressure controls and variable cam timing, all controlled by the computer.

  2. In many gas engines, a throttle plate positioned by an electric motor is used (See Figure 4) , but in some more advanced systems, there is no throttle plate and the amount of air admitted is completely controlled by the timing and lift of the intake valves; again, computer-controlled (BMW’s big 750 and 760Li and the new “3” series are examples of vehicles using this technology).

Those of us who can be dated by remembering cars operated with “spark, mixture and throttle” controls on the wheel or who fly private piston-powered aircraft can appreciate the value of instant and, in some cases, anticipatory adjustment of these critical elements of engine operation.

Finally, this electronic revolution has now gone past the point where the computer can vary intake and exhaust valve timing and lift by electro-hydraulic control of the cam or cams using engine oil for a true camless engine. Yes, the cam itself is a dead duck in the foreseeable future as International/Navistar has built and run a camless diesel for hundreds of thousands of miles with unprecedented success (see Figure 5).

In simple terms, we have the heavy-duty truck owners and hot rodder’s dream engine all in one black box. We now have the ability to infinitely change the valve opening and closing time, the lift of the valve, the moment that fuel is put right in the cylinder and in what form. There are no more “hot” cams with no low end, no more 15-18 speed gearboxes to bootstrap diesels with 600 rpm power bands, no detonation or diesel knock at idle, and incredible fuel economy and emissions that were only a bureaucrat’s dreams five years ago.

Imagine an engine that can open and close its valves different amounts at different degrees of crank rotation at any speed, and can control not only the amount of fuel injected but the exact point in the crank’s journey where it will be sprayed directly into the cylinder in a precise pattern. This is a far cry from hoping that the right mixture will wander down the intake manifold at the right time, hopefully to be ignited by a weak spark timed by mechanical and vacuum “advances,” or that the clock works in the mechanical fuel injection and will have the right answer for the load and speed requirements at that moment when the truck hits the bottom of the big hill.

This concept goes even further, so that multiple injections of different amounts of fuel at different times can be achieved. This means that at idle the timing can be retarded and a light injection can take place in one or more instances, keeping the cylinder and piston warm and ready to work, the catalytic converter hot and the idle smooth (and quiet, in a diesel). When load is applied, the whole game can change in an instant and the timing, injection and amount of air and/or boost can be anticipated and delivered as needed. Similarly, while running at higher rpms at light load, the least amount of fuel necessary to keep the load satisfied can be used; again, sent in to work at exactly the right time(s) to maximize efficiency and minimize emissions. This also works great with cylinder disabling such as that found on the new Chrysler Hemi and some Mercedes and BMW engines.

Injection quantity and quality are the key in emissions strategies; multiple injections of different quantities of fuel at different points in the crank rotation govern the burning of the fuel and the power and pollutant outputs. For example, a little whiff to start the fire and warm up the piston crown, a bigger dose to get the fire burning really hot, a big squirt just before the pressures peak in the combustion chamber and a final whiff to catch any air that was not already burned as the piston races to BDC. These strategies are not different for gas and diesel; just the details are ironed out for each engine and application.

This can mean 95% of available torque just off idle, no pumping losses at light load and high rpm, any kind of power curve you want for your application, and the ability to make one basic engine architecture serve many different vehicles and needs. This has been the rule in diesel for some time, one displacement and “package envelope” can be rated to develop 250 or 550 horsepower with any power and torque curve you want. This commonality will go a long way to making the wizardry cost less as it makes up for the cost of several engine sizes for different uses.

In essence, from the times of steam where the “engineer” could control the steam pressure, steam temperature, valve timing and valve lift; through the “spark, mixture and throttle” controls of the ’20s and the hundreds of different carburetors, ignition systems and fuel injection pumps with all sorts of mechanical or hybrid add-on controls, the events in an engine were always a compromise born of the need for power and control. “Nothing is perfect” could best describe this system of thought, so the best compromise for the most likely to be encountered conditions was the rule.

That was the past. Today, not only does the computer figure out what the load and speed needs are and the emissions restrictions, but it “learns” the operating conditions and driving habits of the user and makes new plans as it operates. In addition, the computer talks and listens to the computers that run the transmission — or in the case of heavy equipment, the hydraulics as well — so that every question is not only answered, but anticipated as well. The computers learn how to match the “spark, mixture and throttle” for every condition, just like when Grandpa advanced the spark and richened the mixture at the bottom of “Three Mile Hill” so that his Model T had plenty of power to make the top without knocking or overheating. Now as the technology advances even further, even engine wear, rolling resistance and other load shapes will be accounted for in the question-and-answer sessions constantly taking place between the computers and the sensors.

Continuous Advances
Unfortunately, the downside to this great new age to some in the industry is the computer. When the old shop boss asked the whiz kid where the grease fittings and adjustment screws were on the new process computers, he was only partly joking. It is very difficult to diagnose and fix something you can’t see or measure. My mechanical engineer grandfather — who successfully made the jump from steam to diesel on the railroad — used to say, “with a steam locomotive it took 10 minutes to find the problem and 10 men and 10 hours to fix it — on a diesel electric, the opposite was the case.” You can’t fix it when you can’t find what is broken.

Where this leaves all of us in the aftermarket is that without the key to the computer vault where the information that makes everything work lives, we cannot fix, rebuild or test our work after installation or on the dyno stand. This is great for the OEMs; if they keep the codes secret, then they can control the repair industry and they have the government as their partner and personal policeman.

In the last big battle between the OEMs in the engine business and the EPA, the deal was that the emissions limit timetables were kept at a compromise, but the government bought the OEM line that “only the OEMs should be trusted with the computer codes to protect the environment” from the rest of the industry and the users.

Unfortunately, a very high percentage of Congressional staffers and EPA employees are lawyers or others with no technical background and they bought into this concept and wrote it into the regulations…a perfect example of the Golden Rule: those with the gold (OEMs) make the rules. It gets worse. In many instances, the OEMs are going to court and winning consent settlements that state that the codes and repair information are “trade secrets” or “proprietary” and thus, if put into the light of day for everyone’s use, the OEMs would be out of business and the black skies would resemble nuclear winter from the uncontrolled emissions of improperly repaired/rebuilt engines due to improper use of the computer codes.

In this country however, the laws are made and enforced by lawyers and others who don’t always understand (or aren’t interested in understanding) the technology and thus take the safe route and may believe the OEM line(s): better to put the bat to some repair shop or rebuilder than risk the “end of life as we know it” due to exhaust pollution.

Imagine that it is three years from now and you are looking at the top of an engine with the “valve cover” off. All you can see are two rows of solenoids and hydraulic actuators, some pipes and injectors, and a lot of wires. A computer is clamped to the engine or on the firewall with a diagnostic plug. The spark plugs have individual coils and a simple harness, or if it’s a diesel, maybe some turbo controls as well. It does not run right and you have no way to even diagnose the problems — there are no grease fittings on the computer.

The aftermarket has unprecedented challenges today. In the past it was tough enough to just keep up with new technology and master it to keep customers happy; today not only is the technology virtually merging between main engine types, but it is being kept away from the industry by the government and the OEMs. In summary, not only do we have to learn, but we have to fight for the right to learn as well.

Did You Know…
Today’s clean diesels typically use a common-rail fuel injection system with variable injection timing. Electronically controlled high pressure injectors release the precise amount of fuel at just the right moment. On GM’s Duramax diesel engines, for example, the system operates at 27,500 psi (1,900 BAR).
Calculated Injection
For a diesel engine to run smoothly, the point of injection must be timed very carefully otherwise the engine will clatter and emit excessive smoke in the exhaust. On older diesel engines, a high pressure mechanical injection pump is timed much like a distributor by rotating its index position with respect to the camshaft.

On newer diesel engines with electronic controls, there is still a high pressure pump but injection timing is controlled by the powertrain control module (PCM). Inputs from a crankshaft/camshaft position sensor and injection control pressure sensor are used to calculate injection timing. The result is much cleaner, quieter combustion without the annoying idle rattle and smoke that’s usually associated with a diesel engine.

Particulate Technology
One of the keys to reducing diesel emissions even more is to use a “particulate trap” in the exhaust. Like a filter, a particulate trap can reduce soot in the exhaust by 80% to 90%. But traps eventually plug up and need to be cleaned periodically.

One way to reduce the need for maintenance is to also use an oxidation catalyst ahead of the particulate trap. By reburning hydrocarbons in the exhaust (much like the catalytic converter in an automobile), particulates can be reduced before they reach the trap along with oxides of nitrogen. But to work efficiently, exhaust catalysts require low sulfur fuel (30 parts per million or less).

Clean diesel technology that uses a catalyst and particulate trap doesn’t work well with today’s high sulfur diesel fuel in the U.S., but new EPA regulations for 2007 will reduce the amount of sulfur that’s allowed in diesel fuel and may open the way for retrofitting many existing diesel engines with converters and particulate traps. If this happens, retrofitting converters could create new business opportunities for your shop.

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