Is Diesel Power In Your Fleet's Future?

Recently, diesel engines have been moved to the forefront as possible substitution power plants for automobile application. Older passenger car diesel engines would not have made this a very palatable alternative. However, re­cent design advances in diesel engine technology have allowed not only the elimination of nearly all of the engine's previous deficiencies, but improve­ments in fuel efficiency and drastic re­ductions in the cost of producing this power plant.

This article will discuss why diesels historically have not been popular and the design improvements that have changed this. It will also cover some additional points of information that will be helpful to you, the fleet opera­tor, in your future decision-making concerning these diesels.

Now, into the details of why diesel engines have not been used in passen­ger cars and light trucks to date, and what is happening that will allow this application. Most of us are aware of diesel engines in their truck applica­tion, and we know that they make a lot of noise and that they apparently require a very skilled operator to drive them efficiently. Many of you are probably also aware that there have been diesel passenger car applications for many cars, such as the Mercedes Benz cars, French Peugots, and many other European makes.

The major drawbacks of these ap­plications have been that: (1) they were sluggish and put out very low horse­power, (2) they were noisy, (3) they had a heavy diesel fuel odor, (4) they frequently had black smoke exhaust, (5) they were of very high weight con­struction, and as a result cost a con­siderable price premium over a gaso­line engine vehicle, and (6) with heavy oil dilution, they required very fre­quent oil changes. (If these oil changes were not rigorously adhered to, the re­sult would be early failure in the life cycle of the engine.)

These previous passenger car en­gines were designed basically after large diesel truck engines. Hence, their characteristics were the same. They typically had excellent low RPM pull­ing characteristics, but were very sluggish to drive under freeway driving conditions. They gave reasonable fuel mileage, but still it would take 100,000 to 150,000 miles without an overhaul to justify the cost penalty.

The situation is quite different now. Suddenly, GM and Volkswagen have modern, high-speed diesel engines, and the latter is only a $170 price prem­ium over the gasoline engine. What has happened to allow this? Well, it will be necessary to get a little technical for a good explanation, but please follow along as we won't get too deep.

The actual technological advance­ments are the careful application of pre-chambers and swirl chambers along with advanced piston design and fuel metering control. Pre-chambers and swirl chambers are very similar, but not identical to the pre-chambers used in the stratified charge (CVCC) engine that Honda uses in its Civics and Ac­cords. In a diesel engine they can sig­nificantly slow clown the burning rate of the fuel in the combustion chamb­ers.

What is the benefit of this slower burning rate? It has many benefits. First and foremost, it reduces the peak pressure loads on the engine's internal parts down to those of a gasoline en­gine. This means that the manufac­turers can now convert an existing gasoline engine into a diesel configura­tion with relatively minor modifica­tions. This significantly reduces the cost of manufacture.

The next important point is that this slow burn rate allows the engine to be revved to the same high RPMs as a gasoline engine. This in turn allows more of the same kind of driveability and horsepower that the gasoline en­gine has.

There are many more significant benefits. Remember the oil dilution problem mentioned earlier? Good combustion control significantly re­duces the soot formation inside an en­gine. This, combined with the tighter internal engine clearances (allowed by the reduced internal engine stress and advanced pistons), can result in an oil dilution situation comparable to that of a gasoline engine. Volkswagen has 7,500 mile oil change intervals on its new diesel, based on the old "CC" oil spec. It could very probably go double this on the standard "SE" oil that is nearly the only oil that you can now get here in the U.S. Volkswagen indi­cates that under its full load bench en­durance tests that its diesel has twice the engine life of its gasoline engine. (This excellent oil dilution control may not be true for all of the new diesels as they come into the marketplace, as they may not have the combustion quality control or the advanced piston design of the Volkswagen engine. This is an area to closely examine as the manufacturers release their data.)

If these benefits weren't enough, here are some more. This slower burn rate has also eliminated the traditional diesel knock. Most modern, new pass­enger car designs will knock only at cold start-up idle. When one is warmed up and being driven, an unsuspecting passenger or driver may not even know it is a diesel. The swirl chamber also has excellent smoke emission control with a more conventional pre-chamber not being quite as good.

That is enough of the advantages that these new slow burn engines have. There are also some other related tech­nologies that have helped the diesel passenger car to blossom. The diesel smell that was also mentioned earlier has been significantly reduced by the evaporative emission control systems necessary as emission requirements for the gasoline engines. More specifically, these evaporative emission control sys­tems seal up the fuel tanks very tight­ly, and as a result, keep the odors in. Hence, there is much less diesel fuel odor.

One more technology point that has allowed this diesel passenger car development is improved fuel control systems. The actual throttle control has been changed to a system that allows throttle response comparable to that of a carbureted gasoline engine.

We have come through a point by point discussion of what the draw­backs of diesels have been and what advances have been made to overcome these drawbacks. What is going to hap­pen now or in the near future that will affect you and your fleet operations? This is not easy to precisely zero in on, but here are some generalities to work with. First, nearly every major car­maker in the world now has a serious diesel program underway. Here in America, we have the GM 350 V-8 diesel, and it is well known that Chrys­ler is working on a diesel version of its 225 CI Slant 6.

Ford has also recently stepped up its diesel activity, and can rapidly accelerate its efforts in this area with the aid of its European branch­es. American Motors is already build­ing Volkswagen-engined Gremlins, and the diesel would be a simple replace­ment for the gasoline engine. In addi­tion, they have just announced a Perk­ins diesel engine option in their Eur­opean Jeep CJs.

The economics of operating these diesels will depend largely or mostly on the cleverness of the adaptation of the gasoline engine to the diesel con­figuration. In spite of being able to use the gasoline engine for the most part, a few more costly components are re­quired. These include a relatively ex­pensive diesel fuel injection system and moderately more expensive cool­ing systems for increased cooling capability. Larger starter motors and bat­teries will also be necessary to crank the extremely high compression ratio. Volkswagen's preliminary price prem­ium for the diesel is $170, and GM's is approximately $1,000. It would be reasonable to expect that the premium should be $1,000 or less.

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What kind of application will bene­fit from these diesels? The historic answer to this is that diesels are at their most advantageous operation at heavy city stop and go traffic. How­ever, Volkswagen's Rabbit diesel show­ed 52 miles to the gallon on the EPA highway cycle, compared to 37 miles per gallon for the gasoline Rabbit.

Even more impressive is its Economy Diesel Rabbit, which has shown an incredible 65 miles to the gallon. Even GM's V-8 diesel is showing 29 miles per gallon on the highway cycle com­pared to 21 for the 350 Oldsmobile 4-barrel engine. It should be noted that these EPA highway mileages are not realistic figures for what to expect in actual vehicle operation, but they are good laboratory numbers for com­paring various vehicles' fuel consump­tion performance.

This leads one to conclude that these diesels will have fuel economy ad­vantages both in town and on the high­way. With GM talking about a 25-per­cent overall improvement, the econ­omics then become fairly simple. It will be a matter of determining what vehicle mileage is necessary to write off the diesel's price premium with the applicable fuel cost savings.

Diesels do not require the same kind of tune-ups that gasoline engines require, and it is possible that they might cost less for routine mainte­nance. However, gasoline engines are requiring less and less maintenance, and diesels do require other kinds of periodic maintenance. Hence, there may or may not be a routine main­tenance cost savings. Of course, it is also possible that diesel engines may suffer less price depreciation in the future than gasoline engines. However, one would not want to count on that this early in the game.

The Economy Diesel Rabbit uses an overdrive transmission to achieve its 65 miles per gallon highway rating, and this is an important aspect to understand about diesels. They re­spond to a high, overdrive type of gearing even more so than a gasoline engine. This is because of their excel­lent low RPM torque characteristics. An equal size diesel engine will pro­duce less horsepower than a gasoline engine, and it will be tempting to go to lower gearing (higher engine speed) to compensate for the loss of acceleration capability. A fleet operator seriously interested in reducing his fuel consumption should opt for the higher, overdrive type of gearing.

The mechanical reliability of these new diesels will be mostly related to the fuel injection system. The basic en­gine should be able to considerably outlast the comparable gasoline engine. The potential problems with the fuel injection system are in the pump, throttle control system, and the injectors. Diesel components have traditionally been made to conform to very long life specifications, but it would be wise for the fleet operator to keep abreast of any "teething" problems that any particular manufacturer may be experiencing.

Now that we have covered most of the technical aspects, let's briefly cover the emission aspects of a diesel and what kind of impact they will have on availability. The problem here is with NOx emissions (oxides of nitro­gen). The initial Federal Muske emis­sions laws stated that all engines must not exceed 0.41 grams per mile emis­sions of NOx after 1976. American manufacturers have had little success with conformity here, and the require­ments have been yielded to 2.0 grams per mile, temporarily. Current technol­ogy only allows diesels to get down to 1.5 grams per mile (with Volkswagen's small Rabbit diesel perhaps getting 1.0 grams per mile.) In a gener­al sense, the diesel is currently equal to gasoline engine NOx emissions, and the likely outcome of the situation will not be whether or not diesels can be used, but how large (how much horsepower) diesel engines will be. This is because NOx increases with horsepower output. Of course, further advances in technology would go in the diesel's favor. From a practical standpoint, the availability of diesel fuel at convenient locations will likely be of more concern to the fleet oper­ator.

One final comment is about the cold starting characteristics of diesel engines and their economics in cold weather operation. Diesels require glow plugs to start in very cold weath­er, and coping with these is nothing more than a driver learning to wait for a red light to go out before he at­tempts to start the engine. This char­acteristic of diesels has tended to scare some operators from the use of diesels in extremely cold environments. How­ever, the diesel is really at its best in comparison with the gasoline engine in cold weather operation. Gasoline en­gines require extreme enrichment to be able to operate while the engine is being operated cold. This extreme en­richment can bring the mileage of a V-8 to only 4 to 5 miles per gallon while the choke is on. A diesel engine, on the other hand, requires no cold en­richment. It operates with its same fuel-stingy characteristics as when it is warm. The fuel savings with diesels that are frequently cold started will be significantly above that of conditions when the vehicles are normally warm-started.

These new diesels have extremely high compression ratios (22.5 to 1 and higher). The reason for this is the be­low 0° C. cold start. The best compres­sion ratio for fuel economy is in the 17 to 1 area, but a higher compression ratio is necessary to allow the engine to start and stay running when it is be­low 0° C. Fuel economy should im­prove even more if this handicap is overcome with future development work.

Few fleets will be making decisions on these new engines this year. But in the years to come, it will be important for the fleet administrator to become increasingly knowledgeable of these new diesel power plants.

GM has given its corporate blessing to the Oldsmobile Division to become the "Diesel Division" - at least for now. Olds will have two luxury sedans with diesel power this fall with Chevy and GMC sharing the engine in pickup models. All these plans hinge on the factory-EPA-Congress relation­ship and the ruling on diesel emissions. And time is short in Lansing, home of Olds.

The obvious objective in the move to diesel is fuel eco­nomy, and it appears that the Olds Delta 88 is clearing the magic 20-mph hurdle for both city and highway EPA test driving.

The new Olds Diesel is efficient enough to decisively de­velop both fuel economy and power compared to two con­ventional gasoline engines. From the following chart it appears that the diesel produces an increase of 25 percent in economy compared to the equivalent horsepower gas engine.

From what is known today, the Olds Diesel has charac­teristics of complete dynamic balance of all moving parts that rates as an improvement over current day smaller die­sels. It has a cast-iron block from its gasoline engine block parentage for both durability and ignition noise suffocation.

The compression ratio is reportedly 22.5 to one in this 350-cubic-inch V-8 with all new cylinder heads and the swirl-type combustion chambers. Glow-plugs (preheaters) will be utilized as a cold-starting assist. Beefing up the pis­tons, connecting rods and wrist pins as well as providing more capacity in the starter, battery and alternator were necessary.

The fuel-injection system is a tried and true one serving millions of diesel engines in both off-highway vehicles and industrial applications. It is produced by Roosamaster Pro­ducts Division of Stanadyne and is of a rotary (vs. the Robert Bosch in-line) injection design with a single set of plungers rotating in a fuel distributor-head lending another production cost advantage and compactness in overall de­sign.

Acceleration with the 135 horsepower plant is said to be a remarkable 0-60 in 16 seconds compared to 21.7 seconds for the '77 Mercedes-Benz 300D. Even the oil marketers are now gearing for more diesel pumps as GM is readying to produce (and sell) 100,000 diesels in the next model year.