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The Cummins A3.4-125 (rated 93 kW at 3600 rpm) has been developed to meet 1991 US and California light-heavy duty emission standards, replacing the Cummins 6AT3.4 (formerly Onan L634T-A). Compliance with the stringent particulate standard has been achieved by redesigning the combustion chamber, a systematic oil control program, and charge air cooling. The Ricardo Comet combustion chamber was modified to a downstream glowplug configuration. Oil control efforts addressed all sources of oil derived particulate. With charge air cooling, NOx emissions were reduced while improving fuel economy, torque output, altitude capability, and engine durability. THE CUMMINS A3.4-125 is an evolutionary development of the 1988-90 6AT3.4 engine. The development was driven primarily by 1991 US and California light-heavy duty emission standards, but also was the result of a policy of continuous product improvement. The Cummins A Series diesel engine family was conceived as the Onan L Series (1*).

A high horsepower, low heat rejection diesel engine is being developed to meet future Army heavy combat vehicle requirements. This engine features high power output in a compact design that is oil-cooled allowing for a significant reduction in radiator size. This design requires a lubricant which can survive a sump temperature of 160°C, for 300 hours with transient sump temperature surges to over 177°C. A comprehensive high temperature lubricant development program has been initiated to address the need for this new design. A modified Cummins 10 liter diesel engine was used to simulate the operating condition of this low heat rejection engine. The premium commercial lubricant that was tested survived only 58 hours before completely losing oxidative stability. Several of the experimental lubricants completed the 200-hour peak torque endurance test.

Corrosive wear of non-ferrous engine components by lubricants is a concern of all major heavy duty diesel engine manufacturers since warranty on key engine components has been extended to 500,000 miles. Several commercial lubricants have been linked to premature cam and rod bearing failures induced by corrosion in certain fleets. Although the overall failure rate is low, specific fleets have experienced significantly higher failure rates due to the lubricants used. These failures usually occur at high mileages but less than 500,000 miles. This kind of slow corrosion easily escapes detection of engine tests contained in current oil specifications, and it represents a serious issue in long term warranty cost to diesel engine manufacturers. A comprehensive fleet database has been established to identify the most corrosive lubricants. These lubricants have served as reference oils to develop a corrosion bench test.

An engine rig test and a scuffing BOCLE test have been used to investigate the lubricity of low sulfur diesel fuels and its relationship with unit injector wear in heavy duty diesel engines. The rig test effectively ranks 11 selected fuels/fluids according to their actual performance. The scuffing BOCLE test correlates with the rig test by showing the same ranking capability, and it is easy to perform. A similar correlation has been established using ISO reference fuels. The scuffing BOCLE test has been used to study 37 fuels randomly sampled from the field. The data shows that there is indeed a reduction in lubricity of low sulfur fuels. The variation in lubricity of low sulfur fuels is also much greater than high sulfur fuels. Data in this study shows that transition from good to poor lubricity usually occurs between 2500 to 3000 grams in the scuffing BOCLE.

Reports of disabling diesel engine seal failures which accompanied the introduction of low sulfur diesel fuel in October '93 prompted an in-depth survey of diesel fuel chemical and physical properties. The purpose of the survey was to anticipate other possible problems which might arise with the newly introduced low sulfur fuels. The survey will produce a database containing over 1000 number 2 diesel fuels from various parts of the US. About 75% of the samples tested were on-highway low sulfur diesel fuels. Samples analyzed were from the D-A Lubricant Company, Cummins customers failures (truck fleets of various sizes), and a number of retail fueling stations. Properties under investigation are % Sulfur, Cloud/Pour Points, Viscosity, API Gravity, TAN/TBN, Boiling Range, Aromatics content, Heat Content, Lubricity, and Peroxide number.

The ability of a piston oil ring to conform to liner distortions during engine operation is directly related to its radial stiffness. The ability to conform is also very important for controlling lubricant oil consumption and emissions. This paper describes the procedure utilized to investigate the technical feasibility of using flexible high performance engineering plastics to replace metal as base material for oil rings. Bench tests and engines were used to select and evaluate different types of plastics for wear resistance and structural integrity. Engine test results indicated no structural failures but wear levels were found to be unacceptably high for use in durable heavy duty diesel engines.

Diesel engine builders are faced with a new challenge to lower the weight of engines to increase payload while meeting rigorous durability goals for the engine. Cooling system parts represent a family of components which may be converted to lightweight metallic alloys for significant weight savings. To utilize lightweight alloys, cooling system parts must be engineered to maintain the same durability as the cast iron components they replace. For a modern high speed diesel, the Bl0 design life may be upwards of 1,280,000 kilometers which is a very aggressive target for a new component design. A test program was planned to guide design and development of aluminum (Al) cooling system parts for a new engine. The part must exhibit no corrosion after long duration operating with acceptable coolant. This program included three major phases consisting of bench scale corrosion tests for alloy selection, component rig tests for design verification and engine testing for system reliability.

Evolving diesel engine design trends are expected to include fuel systems operating at significantly higher pressures and temperatures than in the past. Accordingly, meaningful laboratory tests are needed to help guide this development. Two candidate test methods were evaluated in this exploratory study. Scuffing Load Ball-on Cylinder Lubricity Evaluator (BOCLE) and Modified High-Frequency Reciprocating Rig (HFRR) test results covering a range of operating temperatures were compared with fuel property data. Correlations of the Modified HFRR test data with BOCLE results were also made.

High Velocity Oxygen Fuel sprayed face coatings have shown great promise for piston rings used for High Power Density Diesel Engines. Various coatings have been tested on both wear test rigs and in engines. A highly dense HVOF cermet coating was developed with reasonable crack resistance during service. The HVOF coated piston rings wore three to six times lower than chrome plating. Cylinder liner (counter face) wear was found to be one to three times higher than chrome. However, engine oil consumption and blow by were within normal values. The HVOF coating is considered to be an excellent replacement for chrome plating. The coating process is more environmentally friendly than the chrome plating process. Also, the coating has potentially lower or equivalent production cost when compared to chrome.

Compression rings for heavy duty diesel engines are traditionally made of ductile cast iron material. These rings, in general, have conservative standard dimensions limited by the strength of their base material. More recently, however, the market for heavy duty diesel engines demanded products able to cope with high levels of power density and, at the same time, lower levels of oil consumption, friction, and emissions. This paper discusses the advantages of some radical changes made on the design of compression rings in order to take advantage of steel as the base material. The superior mechanical properties of steel allow the use of rings with smaller cross sections which minimizes the friction losses caused by the combustion gas pressure pushing the ring against the liner. It also allows the use of compression rings with a free gap significantly larger than usual.

Laboratory tests have shown that 40% glass-reinforced PPS is suitable for automotive underhood use where it comes into contact with used engine oil, gasoline/alcohol, gasoline/MTBE, water, water/ethylene glycol, hydraulic fluid, and transmission fluid at elevated temperatures. On exposure to water or water/ethylene glycol at 248° F (120° C) and 257°F (125°C), respectively, there is a sharp decline in mechanical strength in the first few weeks with little change thereafter. The residual strength of the 40% glass-reinforced PPS is comparable to, or better than other materials, such as phenolics, which have proved satisfactory in such usage. These results have been translated to successful applications in heavy duty diesel engines. Piston cooling nozzles and water pump impellers made of 40% glass-reinforced PPS have undergone successful engine component evaluations.

There has been an accelerated growth in power of diesel engines in United States line haul trucking. This paper analyzes the effect of high power on engine-related operating variables that occur under different highway conditions and dissimilar terrain features. When properly applied, high-powered diesel engines can increase average vehicle speed and/or fuel economy.

Tests were conducted with several production diesel engines and one prototype low-emission diesel engine to determine the effect of fuel properties on exhaust emissions and engine performance. Fuel cetane number was found to be the most significant fuel property; low cetane fuels resulted in higher hydrocarbons and oxides of nitrogen and increased noise. Conversely, higher cetane fuels produced lower emissions and noise, and also improved engine starting characteristics. The degree of these effects was influenced by engine configuration. Although engine design changes can result in substantial emissions reduction, fuel properties can also influence achieveable levels.

The ongoing need for improved fuel economy, longer engine life, lower emissions, and in some cases, increased power output makes lower charge air temperatures more desirable. In 1983, Cummins introduced the new BCIV engine at 400 H.P. (298 KW) with “Optimized Aftercooling”, and is now introducing this concept to its remaining 10 and 14 Litre premium diesel engines. This Tuned Low Flow Cooling design provides many advantages when compared to the other alternatives studied, which included air-to-air and systems incorporating two radiators. The selection process considered performance, durability, fuel economy, emissions, noise, investment, and total vehicle installed cost. Computer simulations and vehicle tests were used to determine performance for each charge air cooling alternative. The simulations were used to guide prototype development and the selection of production hardware.

Warranty data can be a useful, accurate, and timely information source for monitoring the reliability of a product. At Cummins Engine Company a warranty based reliability information system was developed for diesel engines that has the capability to 1) evaluate the reliability of engines and their components, 2) compare the reliability performance of engines and components to goals and prioritize those areas needing improvement, and 3) detect changes in the warranty claims pattern of engine components to provide early warning of potential problems. This paper will describe this warranty data system with emphasis on the analytical tools used to perform the above activities. Although many of the examples refer to diesel engines, the general concepts apply to the use of warranty data for many types of products.

The entire engine lubrication system has been represented by a series-parallel network of flow passages and flow elements. The pressure distribution and flow rates in the network were computed according to pressure-flow characteristics of each element. The pressure-flow relationship for each network element was estimated using empirical pipe friction, expansion, and bend loss coefficients, as well as by using test rig results and a steady-state journal bearing model. The journal bearing model is basically that of the classical short bearing model with provision for heat transfer to the oil and the relative thermal growth of the journal and bearing system. When compared with diesel engine tests, the simulation predicted the pressure distribution throughout the engine and the flow rate through each branch within 10%.

Measurements of instantaneous temperature were made at three locations on the cylinder head of a direct injection diesel engine. Changes in calculated instantaneous heat flux with changes in cylinder head surface temperature were assessed. The results were used in an assessment of various approaches to the description of instantaneous heat transfer incorporated in diesel cycle simulations. It was concluded that changes in the thermal boundary layer thickness throughout the cycle could account for some of the observed phenomena. A close correlation was seen between the heat transfer measured here and earlier published studies of measured boundary layer thickness. Some additional indications from the measurements point to a significant thermal capacitance of the boundary layer. Additional work is needed to further understand the potential ramifications of this effect.

A Cummins B55 in3 350 bhp heavy-duty, turbocharged diesel engine was tested in fully cooled and uncooled modes over the EPA transient emission test cycles for comparison of gaseous and particulate emissions. The results are presented at the same fuel injection timing and at similar NOx emission levels. Also, steady state emission measurements and analysis of real-time transient emission data of selected runs are discussed. The uncooled engine does not represent an adiabatic (insulated) engine in its emission characateristics, but may indicate some trends. It may be useful in identifying design and/or operating parameters that need optimization.

Diesel engine operation under high load conditions (>45 hp/cyl) may result in piston “debond” in which the Ni-resist ring carrier separates from the aluminum piston matrix leading to destruction of the piston. Historically, engine loads have increased to achieve higher power densities which together with more stringent emissions requirements have resulted in greatly increased stress levels in the piston. The higher stresses have resulted in debond failure. The design of the ring carrier will affect debond failure. Deformation of the ring carrier will initiate debond at the back of the insert at the junction with the piston matrix. The ring carrier cross-section must be made robust enough through proper design to achieve expected reliability. Another factor influencing ring carrier retention is the quality of the AlFin bond layer. Casting defects which arise from the AlFin bonding process, degrade the strength of the joint leading to failure.