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The Euro IV legislation for heavy-duty on-road vehicles enforces emissions limits on the tailpipe NOx levels during both transient and modal testing, typically paired with additional limitations on, for example, ammonia emissions. There are several possible strategies for complying with the legislation, including engine management measures as well as after-treatment in the form of catalytic removal of NOx with ammonia as the reducing agent. Based on experimental data, a range of important aspects are presented and discussed, with both overall system performance and the installation and operational costs in mind. Factors relevant for future legislations, in the form of EU V and beyond, are also discussed. Operating the engine with high levels of Exhaust Gas Recirculation (EGR) is a possible path to EU IV compliance with no or little catalytic NOx reducing after-treatment. Here, it is contrasted against an SCR-only solution based on a non-EGR engine calibration.

The Selective Catalytic Reduction (SCR) catalyst with ammonia as reducing agent plays a central role in today's exhaust after-treatment systems for heavy-duty vehicles and there is a wide selection of possible catalytic materials to use. In order to facilitate the design of future catalysts, several aspects of the materials must be evaluated both in steady-state and transient operation. To this end, this paper presents a methodology for comparing the dynamic properties of different catalysts using full-size engine testing. The studied characteristics include the ammonia storage capacity, the effect of starting with an empty catalyst, the transient response to temperature gradients and changes in the urea dosing level. The temperature response is of particular importance in transient operation, where temperature increases may lead to substantial ammonia slip. A vanadium catalyst is compared to a Cu-SAPO-34 catalyst, and they show significant differences in their dynamic response.

Emissions and in-cylinder pressure traces are used to compare the relative importance of soot formation and soot oxidation in a heavy-duty diesel engine. The equivalence ratio at the lift-off length is estimated with an empirical correlation and an idealized model of diesel spray. No correlation is found between the equivalence ratio at lift-off and the soot emissions. This confirms that trends in soot emissions cannot be directly understood by the soot formation process. The coupling between soot emission levels and late heat release after end of injection is also studied. A regression model describing soot emissions as function of global engine parameters influencing soot oxidation is proposed. Overall, the results of this analysis indicate that soot emissions can be understood in terms of the efficiency of the oxidation process.

Bioethanol is an established biofuel used today in sparked-ignited (SI) engines, however with limited fuel efficiency and stringent requirements on the ethanol purity (water content). In this paper, we will present the operation of a compression-ignition (CI) engine fuelled with upgraded hydrous ethanol. A specific fuel upgrade operation (excluding additives) converts a fraction of the hydrous ethanol to diethyl-ether, hence increases the cetane number up to adequate levels. The resulting upgraded fuel is tested in a commercial diesel engine (light-duty common-rail EURO IV model). In particular, the compression ratio is kept unchanged and only the injection timing is modified to ensure compression-ignition operation, securing the peak pressure at 8-12 degrees after top dead center.

Partially Premixed Combustion is a concept able to combine low smoke and NOx emissions with high combustion controllability and efficiency. It is of interest to be able to utilize PPC in a large operating region in order to meet the Euro VI emission legislation without relying on NOx aftertreatment. This paper investigates the differences in PPC characteristics for three fuels; Diesel Swedish Mk 1, Low Octane Gasoline (70 Octane) and US Standard Gasoline (87 Octane). Engine operating conditions, combustion characteristics, emissions and efficiency are in focus. The experiments were carried out at a range of operating points on a Volvo MD13 which is a six-cylinder heavy-duty engine. At each operating point three combinations of EGR level and λ-value were evaluated. 1. High EGR/High λ, 2. High EGR/Reduced λ, and 3. Reduced EGR/High λ.

Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels and injection timings sufficiently early or late to extend the ignition delay so that air and fuel mix extensively prior to combustion. This paper investigates the operating region of single injection diesel PPC in a multi cylinder heavy duty engine resembling a standard build production engine. Limits in emissions and fuel consumption are defined and the highest load that fulfills these requirements is determined. Experiments are carried out at different engine speeds and a comparison of open and closed loop combustion control are made as well as evaluation of an extended EGR-cooling system designed to reduce the EGR temperature. In this study the PPC operating range proved to be limited.

Partially Premixed Combustion (PPC) has shown its potential by combining high combustion controllability with emission characteristics that are close to those of an HCCI engine. In order to get PPC the ignition delay needs to be long enough for the fuel and air to mix prior to combustion. This can be achieved by injecting the fuel sufficiently early while running with high EGR. In order to find out where and how PPC occurs a map that shows the changes in combustion characteristics with injection timing and EGR was created. The combustion characteristics were studied in a six cylinder heavy duty engine where the Start of Injection (SOI) was swept from early to late injection over a wide range of EGR levels. The emissions were monitored during the sweeps and in the most promising regions, with low emissions and high efficiency, additional changes in injection pressure and engine speed were applied to get a more versatile picture of the combustion.