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Studies have been conducted at Michigan Technological University (MTU) for over twenty years on methods for characterizing and controlling particulate emissions from heavy-duty diesel engines and the resulting effects on regulated and unregulated emissions. During that time, control technologies have developed in response to more stringent EPA standards for diesel emissions. This paper is a review of: 1) modern emission control technologies, 2) emissions sampling and chemical, physical and biological characterization methods and 3) summary results from recent studies conducted at MTU on heavy-duty diesel engines with a trap and an oxidation catalytic converter (OCC) operated on three different fuels. Control technology developments discussed are particulate traps, catalysts, advances in engine design, the application of exhaust gas recirculation (EGR), and modifications of fuel formulations.

The CRC-APRAC CAPI-1-64 Odor Panel was formed in 1973 to assess an instrumental measurement system for diesel exhaust odor (DOAS) developed under CRC-APRAC CAPE-7-68 by Arthur D. Little, Inc. Four cooperative studies were conducted by nine participating laboratories using common samples. The objectives of these studies were to define the DOAS system variables and to validate and improve the sampling and collection procedures. A fifth study, serving as a review of each analysis step, showed that analysis of common derived odorant samples could be conducted within acceptable limits by the participating laboratories. Three in-house sampling system design and operating parameter studies were conducted simultaneously with the cooperative work. The combined findings from the in-house and cooperative studies led to a tentative recommended procedure for measuring diesel exhaust odor.

This is the fourth in a series of tests conducted as a Coordinating Research Council cooperative program to evaluate the measurement methods used to analyze diesel exhaust gas constituents. A multi-cylinder engine was circulated to 15 participants who measured emissions at three engine conditions. All 15 participants measured nitric oxide and carbon monoxide with several laboratories measuring nitric oxide by both NDIR (Non-Dispersive Infrared) and CHEMI (Chemiluminescence). Some participants also measured carbon dioxide, nitrogen dioxide, oxygen, and unknown span gases. The test results are compared with the Phase III cooperative tests which involved simultaneous measurement of emissions by participants. The precision of the results was poorer in Phase IV than Phase III.

A microprocessor controlled lubricating oil cooling system of truck diesel engine was designed to minimize the sump oil temperature fluctuation during start-up and nonsteady engine operations. Model reference adaptive control method is utilized in the control system design. The analysis involved in the design of the microprocessor controlled oil cooling system, and the applications of a special vehicle-engine-cooling system (VEC) computer simulation code in the implementation and testing of the model reference adaptive control strategy are described. Using the VEC simulation code, the performance of the microprocessor controlled oil cooling system and the conventionally controlled oil cooling systems were compared for the ATB, temperature disturbances, and cold weather transient tests. An explanation of each test, as well as a review of the results of comparison tests are presented.

Optimizing the performance of the aftertreatment system used on heavy duty diesel engines requires a thorough understanding of the operational characteristics of the individual components. Within this, understanding the performance of the catalyzed particulate filter (CPF), and the development of an accurate CPF model, requires knowledge of the particulate matter (PM) distribution throughout the substrate. Experimental measurements of the PM distribution provide the detailed interactions of PM loading, passive oxidation, and active regeneration. Recently, a terahertz wave scanner has been developed that can non-destructively measure the three dimensional (3D) PM distribution. To enable quantitative comparisons of the PM distributions collected under different operational conditions, it is beneficial if the results can be discussed in terms of the axial, radial, and angular directions.

As use of Particulate Filters (PFs) is growing not only for diesel but also for gasoline powered vehicles, the need for better understanding of deposit structure, growth dynamics and evolution arises. In the present paper we address a number of deposit growth and restructuring phenomena within particulate filters with the aim to improve particulate filter soot load estimation. To this end we investigate the dynamic factors that quantify the amount of particles that are stored within the wall and the restructuring of soot deposits. We demonstrate that particle accumulation inside the porous wall is dynamically controlled by the dimensionless Peclet number and provide a procedure for the estimation of parameters of interest such as the loaded filter wall permeability, the wall-stored soot mass at the onset of cake filtration.

The research on health effects of soot particles has demonstrated their toxic impact on humans, especially for the smallest ones that can pass through the lungs into the bloodstream and be transferred to other parts of the body. Since the Euro 5b regulation, the total particle number (PN) at the exhaust is limited, but the associated protocol developed by the Particle Measurement Program (PMP) group defined a counting efficiency at the 23 nm cut-off particle diameter to avoid measurement artefacts [1][2]. Recent studies have demonstrated that the last generation Euro 6 engines can emit as many particles in the range 10-23 nm as beyond 23 nm [3]. The SUREAL-23 project (Understanding, Measuring and Regulating Sub-23 nm Particle Emissions from Direct Injection Engines Including Real Driving Conditions), funded by Horizon 2020 EU-program, aims to develop sampling, conditioning and measuring instruments and associated methodologies to extend the existing protocol down to at least 10 nm.

Future diesel emission control systems have to effectively operate under non-conventional low-temperature combustion engine operating conditions. In this work the research and development efforts for the realization of a Multi-Functional catalyst Reactor (MFR) for the exhaust of the upcoming diesel engines is presented. This work is based on recent advances in catalytic nano-structured materials synthesis and coating techniques. Different catalytic functionalities have been carefully distributed in the filter substrate microstructure for maximizing the direct and indirect (NO2-assisted) soot oxidation rate, the HC and CO conversion efficiency as well as the filtration efficiency. Moreover, a novel filter design has been applied to enable internal heat recovery capability by the implementation of heat exchange between the outlet and the inlet to the filter flow paths.

Improved understanding and compact descriptions of the pressure drop evolution of Particulate Filters (both for diesel and gasoline powered vehicles) are always in demand for intelligent implementations of exhaust emission system monitoring and control. In the present paper we revisit the loading process of a particulate filter focusing on a parametric description of the deep bed-to-cake transition in the light of recent progress in the understanding of soot deposit structure, growth dynamics and evolution. Combining experimental data, simulation models and information theoretic concepts we provide a closed-form representation of the entire evolution of pressure drop (from the initial clean state up to the evolving linear cake growth regime) parameterized in terms of the physical parameters of the system (filter and particle structure/geometry and flow properties).

Diesel particulate matter in both the diluted and undiluted state is subject to the processes of coagulation, condensation or evaporation, and nucleation which causes continuous changes in its physical characteristics. The Electrical Aerosol Analyzer (EAA) is used to measure the diesel particle size distribution in the MTU dilution tunnel for a naturally aspirated direct-injection diesel engine operated on the EPA 13 mode cycle. The design and development of accurate and repeatable sampling methods using the EAA are presented. These methods involve both steady-state tunnel and bag measurements. The data indicate a bimodal nature within the 0.001 to 1 μm range. The first mode termed the “embroynic mode” has a saddle point between 0.005 to 0.015 μm and the second mode termed the “aggregation mode” lies between .08 to .15 μm for the number distribution.

Diesel and gasoline direct injection engines emit nucleation mode particles either under special conditions or as part of their normally emitted size distribution, respectively. Currently, European legislation excludes nucleation mode particles as particle number vehicle emission measurements are limited down to 23 nm. The rationale behind such a cut-off size is based on the avoidance of significant uncertainties inherent in the sampling and measuring of sub-23 nm solid particles. However, the sub-23 nm particles have drawn increased attention since a large fraction of particles emitted by modern vehicles lies in this size range. In this study we investigate the possibility of accurate nucleation mode particles detection by using the Advanced Half Mini Differential Mobility Analyzer (HM-DMA).

One of the more objectionable aspects of the use of diesel engines has been the emission of particulate matter. A literature review of combustion flames, theoretical calculations and dilution tunnel experiments have been performed to elucidate the chemical and physical processes involved in the formation of diesel particulate matter. A comparative dilution tunnel study of diluted and undiluted total particulate data provided evidence supporting calculations that indicate hydro-carbon condensation should occur in the tunnel at low exhaust temperatures. The sample collection system for the measurement of total particulate matter and soluble sulfate in particulate matter on the EPA 13 mode cycle is presented. A method to correct for hydrocarbon interferences in the EPA barium chloranilate method for the determination of sulfate in particulate matter is discussed.

A computer simulation model to predict the thermal responses of an on-highway heavy duty diesel truck in transient operation was used to study several important cooling system design and operating variables. The truck used in this study was an International Harvester COF-9670 cab-over-chassis vehicle equipped with a McCord radiator, Cummins NTC-350 diesel engine, Kysor fan-clutch and shutter system, aftercooler, and standard cab heater and cooling system components. Input data from several portions of a Columbus to Bloomington, Indiana route were used from the Vehicle Mission Simulation (VMS) program to determine engine and vehicle operating conditions for the computer simulation model. The thermostat-fan, thermostat-shutter-fan, and thermostat-winterfront-fan systems were studied.

Single droplet theory is used to simulate the behavior of fuel sprays in high-speed open-chamber diesels. A model for sprays in still air is presented which includes the air motion induced by the spray. Calculated paths and vaporization histories for droplets injected into swirling air are also presented. It is shown that the paths of vaporizing drops are closely approximated by solid sphere calculations. The effects of swirl speed, engine rpm, and squish air motion are also investigated.

As demand for wall-flow Diesel Particulate Filters (DPF) increases, accurate predictions of DPF behavior, and in particular their pressure drop, under a wide range of operating conditions bears significant engineering applications. In this work, validation of a model and development of a simulator for predicting the pressure drop of clean and particulate-loaded DPFs are presented. The model, based on a previously developed theory, has been validated extensively in this work. The validation range includes utilizing a large matrix of wall-flow filters varying in their size, cell density and wall thickness, each positioned downstream of light or heavy duty Diesel engines; it also covers a wide range of engine operating conditions such as engine load, flow rate, flow temperature and filter soot loading conditions. The validated model was then incorporated into a DPF pressure drop simulator.

A study of the sources of variability in particulate measurements using the Heavy-Duty Transient Test (40 CFR Subpart N) has been conducted. It consisted of several phases: a critical examination of the test procedures, visits to representative facilities to compare and contrast facility designs and test procedures, and development of a simplified model of the systems and procedures used for the Heavy-Duty Transient Test. Some of the sources of variability include; thermophoretic deposition of particulate matter onto walls of the sampling system followed by subsequent reentrainment in an unpredictable manner, the influence of dilution and cooling upon the soluble organic fraction, inconsistency among laboratories in the engine and dynamometer control strategies, and errors in measurements of flows into and out of the secondary dilution tunnel.