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EGR coolers are effective to reduce NOx emissions from diesel engines due to lower intake charge temperature. EGR cooler fouling reduces heat transfer capacity of the cooler significantly and increases pressure drop across the cooler. Engine coolant provided at 40–90 C is used to cool EGR coolers. The presence of a cold surface in the cooler causes particulate soot deposition and hydrocarbon condensation. The experimental data also indicates that the fouling is mainly caused by soot and hydrocarbons. In this study, a 1-D model is extended to simulate particulate soot and hydrocarbon deposition on a concentric tube EGR cooler with a constant wall temperature. The soot deposition caused by thermophoresis phenomena is taken into account the model. Condensation of a wide range of hydrocarbon molecules are also modeled but the results show condensation of only heavy molecules at coolant temperature.

Premixed low temperature combustion (LTC) in diesel engines simultaneously reduces soot and NOx at the expense of increased hydrocarbon (HC) and CO emissions. The use of biodiesel in the LTC regime has been shown to produce lower HC emissions than petroleum diesel; however, unburned methyl esters from biodiesel are more susceptible to particulate matter (PM) formation following atmospheric dilution due to their low volatility. In this study, the efficacy of a production-type diesel oxidation catalyst (DOC) for the conversion of light hydrocarbons species and heavier, semi-volatile species like those in unburned fuel is examined. Experimental data were taken from a high speed direct-injection diesel engine operating in a mid-load, late injection partially premixed LTC mode on ultra-low sulfur diesel (ULSD) and neat soy-based biodiesel (B100). Gaseous emissions were recorded using a conventional suite of analyzers and individual light HCs were measured using an FT-IR analyzer.

The effect of biodiesel produced from waste cooking oil (WCO) on the soot particles in a compression ignition engine was investigated and compared with conventional diesel fuel. The indicated mean effective pressure of approximately 0.65 MPa was tested under an engine speed of 1200 revolutions per minute. The fuels were injected at an injection timing of −5 crank angle degree after top dead center with injection pressures of 80 MPa. Detailed characteristics of particulate matters were analyzed in terms of transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and elemental analysis. Soot aggregates were collected on TEM grid by thermophoretic sampling device installed in the exhaust pipe of the engine. High-resolution TEM images revealed that the WCO biodiesel soot was composed of smaller primary particle than diesel soot. The mean primary particle diameter was measured as 19.9 nm for WCO biodiesel and 23.7 nm for diesel, respectively.

Dimethyl-ether combustion with pilot injection was investigated in a single cylinder direct injection diesel engine equipped with a common-rail injection system. Combustion characteristics and emissions were tested with dimethyl-ether and compared with diesel fuel. The main injection timing was fixed to have the best timings for maximum power output. The total injected fuel mass corresponded to a low heating value of 405 joules per cycle at 800 rpm. The fuel quantity and the injection timing of the pilot injection were varied from 8 to 20% of the total injected mass and from 50 to 10 crank angle degrees before the main injection timing, respectively. Ignition delay decreased with pilot injection. The effects of pilot injection were less significant with DME combustion than with diesel. Pilot injection caused the main combustion to increase in intensity resulting in decreased emissions of hydrocarbons, carbon monoxide and particulate matter.

Diesel fuel injection system is the most important part of the direct-injection diesel engine and, in recent years, it has become one of the critical technologies for emission control with the help of electronically controlled fuel injection. Common rail injection system has great flexibility in injection timing, pressure and multi-injections. Many studies and applications have reported the advantages of using common rail system to meet the strict emission regulation and to improve engine performance for diesel engines. The main objective of this study is to investigate the effect of pilot-, post- and multiple-fuel injection strategies on engine performance and emissions. The study was carried out on a single cylinder optical direct injection diesel engine equipped with a high pressure common rail fuel injection system. Spray and combustion evolutions were visualized through a high speed charge-coupled device (CCD) camera.

A quasi-dimensional, multi-zone, direct injection (DI) diesel combustion model has been developed and implemented in a full cycle simulation of a turbocharged engine. The combustion model accounts for transient fuel spray evolution, fuel-air mixing, ignition, combustion and NO and soot pollutant formation. In the model, the fuel spray is divided into a number of zones, which are treated as open systems. While mass and energy equations are solved for each zone, a simplified momentum conservation equation is used to calculate the amount of air entrained into each zone. Details of the DI spray, combustion model and its implementation into the cycle simulation of Assanis and Heywood [1] are described in this paper. The model is validated with experimental data obtained in a constant volume chamber and engines. First, predictions of spray penetration and spray angle are validated against measurements in a pressurized constant volume chamber.

Diesel injections with various nozzle geometries were tested to investigate the spray characteristics by optical imaging techniques. Sac-nozzle and VCO nozzle with single guided needle coupled with rotary-type mechanical pump were compared in terms of macroscopic spray development and microscopic behavior. These nozzles incorporated with common-rail system were tested to see the effect of high pressure injection. Detailed investigation into spray characteristics from the holes of VCO nozzles, mostly with double guided needle, was performed. A variety of injection hole geometries were tested and compared to give tips on better injector design. Different hole sizes and taper ratio, represented as K factor, were studied through comprehensive spray imaging techniques. Global characteristics of a diesel spray, such as spray penetration, spray angle and its pattern, were observed from macroscopic images.

A thermophoretic particulate sampling device was used to investigate the detailed morphology and microstructure of diesel particulates at various engine-operating conditions. A 75 HP Caterpillar single-cylinder direct-injection diesel engine was operated to sample particulate matter from the high-temperature exhaust stream. The morphology and microstructure of the collected diesel particulates were analyzed using a high-resolution transmission electron microscope and subsequent image processing/data acquisition system. The analysis revealed that spherical primary particles were agglomerated together to form large aggregate clusters for most of engine speed and load conditions. Measured primary particle sizes ranged from 34.4 to 28.5 nm at various engine-operating conditions. The smaller primary particles observed at high engine-operating conditions were believed to be caused by particle oxidation at the high combustion temperature.

This work reports the development and application of multi-dimensional ignition, combustion and emissions models that account for detailed chemistry and mixing effects in a direct injection engine simulation. A detailed chemical reaction mechanism, consisting of 24 species and 104 reactions, is used for increased accuracy of emissions predictions. Turbulent combustion is represented using a modified Eddy Dissipation Concept (EDC) model to account for mixing effects. The soot model includes all aspects of soot formation and destruction. Particle transport equations are used to realistically track transport of the soot particles formed. All computational sub-models developed in this work have been implemented in a modified version of the KIVA-3V code. In order to illustrate the behavior of the new models, soot and NO emissions have been predicted at different operating conditions by varying injection timing, exhaust gas recirculation (EGR) and injection pressure.

The effect of pilot injection and exhaust gas recirculation (EGR) on premixed charge compression ignition (PCCI) combustion was investigated in a single-cylinder direct-injection diesel engine with low engine speed and low load. The injection timing of PCCI combustion was fixed at 25 ~ 30 crank angle degree before top dead center (°CA BTDC) based on the ignition delay and power output. The level of oxides of nitrogen (NOx) emissions of PCCI combustion was 68% lower than that of conventional diesel combustion owing to the reduction of near-stoichiometric region which is well known as the main source of NOx formation. However, the indicated mean effective pressure (IMEP), hydrocarbon (HC), particulate matter (PM) and carbon monoxide (CO) emissions deteriorated compared with conventional diesel combustion because of early injection, advanced combustion phase and lowered combustion temperature. EGR has been applied to PCCI combustion.

This paper investigated the influence of the injector nozzle geometry on fuel consumption and exhaust emission characteristics of a light-duty diesel engine with 250 MPa injection. The engine used for the experiment was the 0.4L single-cylinder compression ignition engine. The diesel fuel injection equipment was operated under 250MPa injection pressure. Three injectors with nozzle hole number of 8 to 10 were compared. As the nozzle number of the injector increased, the orifice diameter decreased 105 μm to 95 μm. The ignition delay was shorter with larger nozzle number and smaller orifice diameter. Without EGR, the particulate matter(PM) emission was lower with larger nozzle hole number. This result shows that the atomization of the fuel was improved with the smaller orifice diameter and the fuel spray area was kept same with larger nozzle number. However, the NOx-PM trade-offs of three injectors were similar at higher EGR rate and higher injection pressure.

In this work, engine-out particle mass (PM) and particle number (PN) emissions were experimentally examined from a gasoline direct injection (GDI) engine operating in two lean combustion modes and one stoichiometric mode with a fuel of known properties. Ten steady state operating points, two constant speed load steps, and an engine cold start were examined. Results showed that solid particles emitted from the engine under steady state stoichiometric conditions had a uniquely broad size distribution that was relatively flat between the diameters of 10 and 100 nm. In most operating conditions, lean homogenous modes can achieve lower particle emissions than stoichiometric modes while improving engine thermal efficiency. Alternatively, lean stratified operating modes resulted in significantly higher PN and PM emissions than both lean homogeneous and stoichiometric modes with increased efficiency only at low engine load.

Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOx emissions. The presence of a cool surface in the hot exhaust causes particulate soot deposition as well as hydrocarbon and water condensation. Fouling experienced through deposition of particulate matter and hydrocarbons results in degraded cooler effectiveness and increased pressure drop. In this study, a visualization test setup is designed and constructed so that the effect of water condensation on the deposit formation and growth at various coolant temperatures can be studied. A water-cooled surrogate rectangular channel is employed to represent the EGR cooler. One side of the channel is made of glass for visualization purposes. A medium duty diesel engine is used to generate the exhaust stream.

The characteristics of soot particles in an exhaust gas for low temperature diesel combustion (LTC) compared with conventional combustion in a compression ignition engine were experimentally investigated by the elemental and thermogravimetric analysis (TGA). Morphology of soot particles was also studied by the transmission electron microscopy (TEM). From the result of the TGA, the water can be evaporated until about 150°C for both combustion regimes. The soot particles for LTC contained more volatile hydrocarbons, which can be easily evaporated from 200°C to 420°C compared with conventional diesel combustion. The soot oxidation for conventional combustion occurs up to 600°C, on the other hand the particles for LTC is oxidized below 520°C. Elemental analysis showed higher oxygen weight fraction resulted from the oxygenated hydrocarbon for the soot particles in LTC. TEM has shown primary particles to be in a diameter range of 20 to 50 nm for conventional diesel combustion.

The use of exhaust gas recirculation (EGR) in internal combustion engines has significant impacts on combustion and emissions. EGR can be used to reduce in-cylinder NOx production, reduce emitted particulate matter, and enable advanced forms of combustion. To maximize the benefits of EGR, the exhaust gases are often cooled with on-engine liquid to gas heat exchangers. A common problem with this approach is the build-up of a fouling layer inside the heat exchanger due to thermophoresis and condensation, reducing the effectiveness of the heat exchanger in lowering gas temperatures. Literature has shown the effectiveness to initially drop rapidly and then approach steady state after a variable amount of time. The asymptotic behavior of the effectiveness has not been well explained. A range of theories have been proposed including fouling layer removal, changing fouling layer properties, and cessation of thermophoresis.

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.

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.

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.

A key challenge for the practical introduction of dual-fuel reactivity controlled compression ignition (RCCI) combustion modes in diesel engines is the requirement to store two fuels on-board. This work demonstrates that partially reforming diesel fuel into less reactive products is a promising method to allow RCCI to be implemented with a single stored fuel. Experiments were conducted using a thermally integrated reforming reactor in a reformed exhaust gas recirculation (R-EGR) configuration to achieve RCCI combustion using a light-duty diesel engine. The engine was operated at a low engine load and two reformed fuel percentages over ranges of exhaust gas recirculation (EGR) rate and main diesel fuel injection timing. Results show that RCCI-like emissions of NOx and soot were achieved load using the R-EGR configuration. It was also shown that complete fuel conversion in the reforming reactor is not necessary to achieve sufficiently low fuel reactivity for RCCI combustion.

This paper describes a test cell setup for concurrent running of a real engine and a vehicle system simulation, and its use for evaluating engine performance when integrated with a conventional and a hybrid electric driveline/vehicle. This engine-in-the-loop (EIL) system uses fast instruments and emission analyzers to investigate how critical in-vehicle transients affect engine system response and transient emissions. Main enablers of the work include the highly dynamic AC electric dynamometer with the accompanying computerized control system and the computationally efficient simulation of the driveline/vehicle system. The latter is developed through systematic energy-based proper modeling that tailors the virtual model to capture critical powertrain transients while running in real time. Coupling the real engine with the virtual driveline/vehicle offers a chance to easily modify vehicle parameters, and even study two different powertrain configurations.