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Advanced diesel engines developed for the commercial market need to be adapted to the military requirements by OPERAS (Optimizing the injection pressure P, the Exhaust gas recirculation E, injection events Retard and/or Advance and the swirl ratio S). The different after treatment devices, already used or expected to be applied to diesel engines, require feed gases of appropriate properties for their efficient operation. To produce these gases some OPERAS are needed to control the diesel combustion process. Since military vehicles do not need the after treatment devices, the OPERAS of the commercial engines should be modified to meet the military requirements for high power density, better fuel economy, reduction of parasitic losses caused by the cooled EGR system, and reduction of invisible black and white smoke in the field.

More stringent regulations have been enforced over the past few years on diesel exhaust emissions. White smoke emission, a characteristic of diesel engines during cold starting, needs to be controlled in order to meet these regulations. This study investigates the sources and constituents of white smoke. The effects of fuel properties, design and operating parameters on the formation and emissions of white smoke are discussed. A new technique is developed to measure the real time gaseous hydrocarbons (HC) as well as the solid and liquid particulates. Experiments were conducted on a single cylinder direct injection diesel engine in a cold room. The gaseous HC emissions are measured using a high frequency response flame ionization detector. The liquid and solid particulates are collected on a paper filter placed upstream of the sampling line of the FID and their masses are determined.

This work presents the development, validation and use of a SIMULINK integrated vehicle system simulation composed of engine, driveline and vehicle dynamics modules. The engine model links the appropriate number of single-cylinder modules, featuring thermodynamic models of the in-cylinder processes with transient capabilities to ensure high fidelity predictions. A detailed fuel injection control module is also included. The engine is coupled to the driveline, which consists of the torque converter, transmission, differential and prop shaft and drive shafts. An enhanced version of the point mass model is used to account for vehicle dynamics in the longitudinal and heave directions. A vehicle speed controller replaces the operator and allows the feed-forward simulation to follow a prescribed vehicle speed schedule.

An experimental study is performed for homogeneous charge compression ignition (HCCI) combustion focusing on late phasing conditions with high cyclic variability (CV) approaching misfire. High CV limits the feasible operating range and the objective is to understand and quantify the dominating effects of the CV in order to enable controls for widening the operating range of HCCI. A combustion analysis method is developed for explaining the dynamic coupling in sequences of combustion cycles where important variables are residual gas temperature, combustion efficiency, heat release during re-compression, and unburned fuel mass. The results show that the unburned fuel mass carries over to the re-compression and to the next cycle creating a coupling between cycles, in addition to the well known temperature coupling, that is essential for understanding and predicting the HCCI behavior at lean conditions with high CV.

The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity.

Naturally aspirated HCCI operation is typically limited to medium load operation (∼ 5 bar net IMEP) by excessive pressure rise rate. Boosting can provide the means to extend the HCCI range to higher loads. Recently, it has been shown that HCCI can achieve loads of up to 16.3 bar of gross IMEP by boosting the intake pressure to more than 3 bar, using externally driven compressors. However, investigating HCCI performance over the entire speed-load range with real turbocharger systems still remains an open topic for research. A 1 - D simulation of a 4 - cylinder 2.0 liter engine model operated in HCCI mode was used to match it with off-the-shelf turbocharger systems. The engine and turbocharger system was simulated to identify maximum load limits over a range of engine speeds. Low exhaust enthalpy due to the low temperatures that are characteristic of HCCI combustion caused increased back-pressure and high pumping losses and demanded the use of a small and more efficient turbocharger.

The U.S. Army Tank-Automotive Command is developing a future high power, low heat rejection military diesel engine. Performance requirements for the engine result in a predicted cylinder wall temperature of 560°C at the top piston ring reversal location. Thermal stresses imposed on the lubricant will therefore be unusually severe. Midwest Research Institute is developing the tribological system for this engine. A new general concept for high temperature diesel engine lubrication has been formulated. Our concept includes advanced synthetic liquid lubricants, solid lubricant additives, and self-lubricating materials. The lubricants, additives, and materials that have been selected for initial laboratory and engine evaluations of the concept are reported here.

Predicting the effects of transient heat conduction in low-heat-rejection engine components have been analyzed by applying instantaneous boundary conditions throughout a diesel engine thermodynamic cycle. This paper describes the advantages and disadvantages of one-dimensional finite difference and two-dimensional finite element methods by analyzing simple and complicated geometries like diesel bowl-in pistons. Also the performance characteristics of plasma sprayed zirconia, partially stabilized zirconia, and a monolithic reaction bonded silicon nitride ceramic materials are discussed and compared. Finite element studies have indicated that the steep temperature gradients associated with cyclic temperature swings in excess of 400 K may contribute to the failure of ceramic coatings near the corner joining the surface of the piston and the surface of the bowl for bowl-in pistons.

EGR is a proven technology used to reduce NOx formation in both compression and spark ignition engines by reducing the combustion temperature. In order to further increase its efficiency the recirculated gases are subjected to cooling. However, this leads to a higher load on the cooling system of the engine, thus requiring a larger radiator. In the case of turbocharged engines the large variations of the pressures, especially in the exhaust manifold, produce a highly pulsating EGR flow leading to non-steady-state heat transfer in the cooler. The current research presents a method of determining the pulsating flow field and the instantaneous heat transfer in the EGR heat exchanger. The processes are simulated using the CFD code FIRE (AVL) and the results are subjected to validation by comparison with the experimental data obtained on a 2.5 liter, four cylinder, common rail and turbocharged diesel engine.

This study investigates the impact of transient engine operation on the emissions formed during a tip-in procedure. A medium-duty production V-8 diesel engine is used to conduct experiments in which the rate of pedal position change is varied. Highly-dynamic emissions instrumentation is implemented to provide real-time measurement of NOx and particulate. Engine subsystems are analyzed to understand their role in emissions formation. As the rate of pedal position change increases, the emissions of NOx and particulates are affected dramatically. An instantaneous load increase was found to produce peak NOx values 1.8 times higher and peak particulate concentrations an order of magnitude above levels corresponding to a five-second ramp-up. The results provide insight into relationship between driver aggressiveness and diesel emissions applicable to development of drive-by-wire systems. In addition, they provide direct guidance for devising low-emission strategies for hybrid vehicles.

Extending the operating range of the gasoline HCCI engine is essential for achieving desired fuel economy improvements at the vehicle level, and it requires deep understanding of the thermal conditions in the cylinder. Combustion chamber deposits (CCD) have been previously shown to have direct impact on near-wall phenomena and burn rates in the HCCI engine. Hence, the objectives of this work are to characterize thermal properties of deposits in a gasoline HCCI engine and provide foundation for understanding the nature of their impact on autoignition and combustion. The investigation was performed using a single-cylinder engine with re-induction of exhaust instrumented with fast-response thermocouples on the piston top and the cylinder head surface. The measured instantaneous temperature profiles changed as the deposits grew on top of the hot-junctions.

The future of maintaining a superior mobile military ground vehicle fleet rests in high power density propulsion systems. As the U.S. Government desires to convert its powerplant base to heavy fuel operation, there arises the opportunity to incorporate new advanced materials into these heavy fuel engines. These newer materials serve the purpose of decreasing powerplant weight and develop new component designs to take advantage of improved strength and temperature capability of those materials. In addition, the military continues the effort for a non-watercooled Low Heat Rejection (LHR) diesel engine. This type of engine demands the use of ceramic and advanced ceramic composite material hardware. Furthermore, today's higher pressure fuel injection systems, coupled with reduced air/fuel ratio as a means of increasing horsepower to size and weight, will require thermal protection or change in material specification for many of the engine's components.

Thermal barrier coatings (TBC) are perceived as enabling technology to increase low heat rejection (LHR) diesel engine performance and improve its longevity. The state of the art of thermal barrier coating is the plasma spray zirconia. In addition, other material systems have been investigated for the next generation of thermal barrier coatings. The purpose of this TBC program is to focus on developing binder systems with low thermal conductivity materials to improve the coating durability under high load and temperature cyclical conditions encountered in the real engine. Research and development (R&D) and analysis were conducted on aluminum alloy piston for high output turbocharged diesel engine coated with TBC.

The need for a rigorous systems engineering approach to automotive powertrains has been addressed in this work from the perspective of the diesel engine. A high-fidelity engine simulation has been integrated with a total vehicle model for the purpose of reverse engineering the optimal powerplant for a given vehicle mission. Engine parameters have been coordinated between the simulations to develop a framework for total vehicle design. The design strategies discussed in this paper allow engine researchers to set targets for individual system components and to analyze the tradeoffs associated with different vehicle mission objectives. A detailed case study employing these techniques is presented for a conventional vehicle where the most fuel-efficient engine is found that simultaneously conforms to the desired performance criteria.

This work studies the complex interactions resulting from the application and control of Exhaust Gas Recirculation (EGR) on a production heavy-duty diesel engine system, and its effectiveness in reducing NOx emissions. The coupling between EGR, the Variable Geometry Turbocharger (VGT) and the EGR cooler critically affects boost pressure, air/fuel ratio (A/F), combustion efficiency and pumping work. It is shown that EGR provides an effective means for reducing flame temperatures and NOx emissions, particularly under low A/F ratio conditions. However, engine thermal efficiency tends to decrease with EGR as a result of decreasing indicated work and increasing pumping work. Combustion deterioration is predominant at higher load, low speed and low boost conditions, due to a significant decrease of A/F ratio with increasing EGR.

The combustion process in a diesel engine was simulated using KIVA-II, a multi-dimensional computer code. The original combustion model in KIVA-II is based on chemical kinetics, and thus fails to capture the effects of turbulence on combustion. A mixing-controlled, eddy break-up combustion model was implemented into the code. Realistic diesel fuel data were also compiled. Subsequently, the sensitivity of the code to a number of parameters related to fuel injection, mixing, and combustion was studied. Spray injection parameters were found to have a strong influence on the model's predictions. Higher injection velocity and shorter injection duration result in a higher combustion rate and peak pressure and temperature. The droplet size specified at injection significantly affects the rate of spray penetration and evaporation, and thus the combustion rate. Contrary to expectation, the level of turbulence at the beginning of the calculation did not affect fuel burning rate.

An experimental investigation of the effects of ceramic coatings on diesel engine performance and exhaust emissions was conducted. Tests were carried out over a range of engine speeds at full load for a standard metal piston and two pistons insulated with 0.5 mm and 1.0 mm thick ceramic coatings. The thinner (0.5 mm) ceramic coating resulted in improved performance over the baseline engine, with the gains being especially pronounced with decreasing engine speed. At 1000 rpm, the 0.5 mm ceramic coated piston produced 10% higher thermal efficiency than the metal piston. In contrast, the relatively thicker coating (1 mm), resulted in as much as 6% lower thermal efficiency compared to baseline. On the other hand, the insulated engines consistently presented an attractive picture in terms of their emissions characteristics. Due to the more complete combustion in the insulated configurations, exhaust CO levels were between 30% and 60% lower than baseline levels.

Selective Catalytic Reduction (SCR) catalysts used in Lean NOx Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNOx the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation. Experiments to characterize the effect of an LNT deNOx event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NOx reduction capabilities of the catalyst.

Present-day implementations of premixed compression ignition low temperature (PCI) combustion in diesel engines use higher levels of exhaust gas recirculation (EGR) than conventional diesel combustion. Two common devices that can be used to achieve high levels of EGR are an intake throttle and a variable geometry turbocharger (VGT). Because the two techniques affect the engine air system in different ways, local combustion conditions differ between the two in spite of, in some cases, having similar burn patterns in the form of heat release. The following study has developed from this and other observations; observations which necessitate a deeper understanding of emissions formation within the PCI combustion regime. This paper explains, through the use of fundamental phenomenological observations, differences in ignition delay and emission indices of particulate matter (EI-PM) and nitric oxides (EI-NOx) from PCI combustion attained via the two different techniques to flow EGR.

Premixed compression ignition low-temperature diesel combustion (PCI) can simultaneously reduce particulate matter (PM) and oxides of nitrogen (NOx). Carbon monoxide (CO) and total hydrocarbon (THC) emissions increase relative to conventional diesel combustion, however, which may necessitate the use of a diesel oxidation catalyst (DOC). For a better understanding of conventional and PCI combustion, and the operation of a platinum-based production DOC, engine-out and DOC-out exhaust hydrocarbons are speciated using gas chromatography. As combustion mode is changed from lean conventional to lean PCI to rich PCI, engine-out CO and THC emissions increase significantly. The relative contributions of individual species also change; increasing methane/THC, acetylene/THC and CO/THC ratios indicate a richer combustion zone and a reduction in engine-out hydrocarbon incremental reactivity.