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Technical Paper

Reduction of Soot Emissions from a Direct Injection Diesel Engine using Water-in-Diesel Emulsion and Microemulsion Fuels

The emissions from a direct injection diesel engine measured according to the ECE R49 13-mode cycle and as a function of exhaust gas recirculation are compared for diesel fuel without water addition, and for water-in-diesel as emulsion and microemulsion. The effect of water addition on the soot emissions was remarkably strong for both the emulsion and microemulsion fuels. The average weighted soot emission values for the 13-mode cycle were 0.0024 and 0.0023 g/kWh for the two most interesting emulsion and microemulsion fuels tested, respectively; 5-fold lower than the US 2007 emission limit.
Technical Paper

Performance of a Heavy Duty DME Engine - the Influence of Nozzle Parameters on Combustion and Spray Development

DME was tested in a heavy duty diesel engine and in an optically accessible high-temperature and pressure spray chamber in order to investigate and understand the effect of nozzle parameters on emissions, combustion and fuel spray concentration. The engine study clearly showed that smaller nozzle orifices were advantageous from combustion, efficiency and emissions considerations. Heat release analysis and fuel concentration images indicate that smaller orifices result in higher mixing rate between fuel and air due to reductions in the turbulence length scale, which reduce both the magnitude of fuel-rich regions and the steepness of fuel gradients in the spray, which enable more fuel to burn and thereby shorten the combustion duration.
Technical Paper

Optical study of HCCI Combustion using NVO and an SI Stratified Charge

The effects of using an SI stratified charge in combination with HCCI combustion on combustion phasing, rate of heat release and emissions were investigated in engine experiments to identify ways to extend the operational range of HCCI combustion to lower loads. In the experiments an optical single-cylinder engine equipped with a piezo electric outward-opening injector and operated with negative valve overlap (NVO) and low lift, short duration, camshaft profiles, was used to initiate HCCI combustion by increasing the exhaust gas recirculation (EGR) and thus retaining sufficient thermal energy to reach auto-ignition temperatures. Two series of experiments with full factorial designs were performed, to investigate how the tested parameters (amounts of fuel injected in pilot injections and main injections, stratification injection timing and spark-assistance) influenced the combustion.
Technical Paper

Development Experience of a Multi-Cylinder CCVS Engine

A system for stratifying recycled exhaust gas (EGR) to substantially increase dilution tolerance has been applied to a multi-cylinder port injected four-valve gasoline engine. This system, dubbed Combustion Control through Vortex Stratification (CCVS), has shown greatly improved fuel consumption at stoichiometric conditions whilst retaining ULEV compatible engine-out NOx and HC emission levels. A production feasible variable air motion system has also been assessed which enables stratification at part load with no loss of performance or refinement at full load.
Technical Paper

Evaporation of Gasoline-Like and Ethanol-Based Fuels in Hollow-Cone Sprays Investigated by Planar Laser-Induced Fluorescence and Mie Scattering

The evaporation of different fuels and fuel components in hollow-cone sprays at conditions similar to those at stratified cold start has been investigated using a combination of planar laser-induced fluorescence (LIF) and Mie scattering. Ketones of different volatility were used as fluorescent tracers for different fuel components in gasoline-like model fuels and ethanol-based fuels. LIF and Mie images were compared to evaluate to what extent various fuel components had evaporated and obtained a spatial distribution different from that of the liquid drops, as a function of fuel temperature and time after start of injection. A selective and sequential evaporation of fuel components of different volatility was found.
Technical Paper

Effects of Variable Inlet Valve Timing and Swirl Ratio on Combustion and Emissions in a Heavy Duty Diesel Engine

In order to avoid the high CO and HC emissions associated with low temperature when using high levels of EGR, partially premixed combustion is an interesting possibility. One way to achieve this combustion mode is to increase the ignition delay by adjusting the inlet valve closing timing, and thus the effective compression ratio. The purpose of this study was to investigate experimentally the possibilities of using late and early inlet valve closure to reduce NOx emissions without increasing emissions of soot or unburned hydrocarbons, or fuel consumption. The effect of increasing the swirl number (from 0.2 to 2.5) was also investigated. The combustion timing (CA50) was kept constant by adjusting the start of injection and the possibilities of optimizing combustion using EGR and high injection pressures were investigated. Furthermore, the airflow was kept constant for a given EGR level.
Technical Paper

Emission Reduction Technologies for the Future Low Emission Rail Diesel Engines: EGR vs SCR

The EU emission standards for new rail Diesel engines are becoming even more stringent. EGR and SCR technologies can both be used to reduce NOx emissions; however, the use of EGR is usually accompanied by an increase in PM emissions and may require a DPF. On the other hand, the use of SCR requires on-board storage of urea. Thus, it is necessary to study these trade-offs in order to understand how these technologies can best be used in rail applications to meet new emission standards. The present study assesses the application of these technologies in Diesel railcars on a quantitative basis using one and three dimensional numerical simulation tools. In particular, the study considers a 560 kW railcar engine with the use of either EGR or SCR based solutions for NOx reduction. The NOx and PM emissions performances are evaluated over the C1 homologation cycle.
Technical Paper

Transient Responses of Various Ammonia Formation Catalyst Configurations for Passive SCR in Lean-Burning Gasoline Engines under Various Real Engine Conditions.

Passive selective catalyst reduction (SCR) systems can be used as aftertreatment systems for lean burn spark ignition (SI)-engines. Their operation is based on the interaction between the engine, an ammonia formation catalyst (AFC), and an SCR catalyst. Under rich conditions the AFC forms ammonia, which is stored in the SCR catalyst. Under lean conditions, the SCR catalyst reduces the engine out NOx using the stored NH3. This study compared the ammonia production and response times of a standard three way catalyst (TWC) and a Pd/Al2O3 catalyst under realistic engine operating conditions. In addition, the relationships between selected engine operating parameters and ammonia formation over a TWC were investigated, considering the influence of both the chosen load point and the engine settings.
Technical Paper

High Pressure Ethanol Injection under Diesel-Like Conditions

Laws concerning to emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are therefore needed to satisfy these new legal requirements and reduce fossil fuel dependency. One way to achieve both objectives is to partially replace fossil fuels with alternatives that are more sustainable with respect to emissions of greenhouse gas, particulates and NOx. As a first step towards the development of a direct injected dual fuel engine using diesel fuel and renewable alcohols such as methanol or ethanol, we have studied ethanol (E100) sprays generated with a standard high pressure diesel fuel injection system in a high pressure/temperature spray chamber with optical access. The experiments were performed at a gas density of ∼27kg/m3 at ∼550 °C and ∼60 bar, representing typical operating conditions for a HD engine at low loads.
Technical Paper

Dual Fuel Methanol and Diesel Direct Injection HD Single Cylinder Engine Tests

Laws concerning emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are needed to satisfy these new requirements and to reduce fossil fuel dependency. One way to achieve both objectives can be to partially replace fossil fuels with alternatives that are sustainable with respect to emissions of greenhouse gases, particulates and nitrogen oxides (NOx). A suitable candidate is methanol. The aim of the study presented here was to investigate the possible advantages of combusting methanol in a heavy duty Diesel engine. Those are, among others, lower particulate emissions and thereby bypassing the NOx-soot trade-off. Because of methanol’s poor auto-ignition properties, Diesel was used as an igniting sources and both fuels were separately direct injected. Therefore, two separate standard common rail Diesel injection systems were used together with a newly designed cylinder head and adapted injection nozzles.
Technical Paper

HCCI Operation of a Passenger Car Common Rail DI Diesel Engine With Early Injection of Conventional Diesel Fuel

The possibilities of operating a direct injection Diesel engine in HCCI combustion mode with early injection of conventional Diesel fuel were investigated. In order to properly phase the combustion process in the cycle and to prevent knock, the geometric compression ratio was reduced from 17.0:1 to 13.4:1 or 11.5:1. Further control of the phasing and combustion rate was achieved with high rates of cooled EGR. The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 480 cc. An injector with a small included angle was used to prevent interaction of the spray and the cylinder liner. In order to create a homogeneous mixture, the fuel was injected by multiple short injections during the compression stroke. The low knock resistance of the Diesel fuel limited the operating conditions to low loads. Compared to conventional Diesel combustion, the NOx emissions were dramatically reduced.
Technical Paper

Location of the First Auto-Ignition Sites for Two HCCI Systems in a Direct Injection Engine

To elucidate the processes controlling the auto-ignition timing and overall combustion duration in homogeneous charge compression ignition (HCCI) engines, the distribution of the auto-ignition sites, in both space and time, was studied. The auto-ignition locations were investigated using optical diagnosis of HCCI combustion, based on laser induced fluorescence (LIF) measurements of formaldehyde in an optical engine with fully variable valve actuation. This engine was operated in two different modes of HCCI. In the first, auto-ignition temperatures were reached by heating the inlet air, while in the second, residual mass from the previous combustion cycle was trapped using a negative valve overlap. The fuel was introduced directly into the combustion chamber in both approaches. To complement these experiments, 3-D numerical modeling of the gas exchange and compression stroke events was done for both HCCI-generating approaches.
Technical Paper

Spark Assisted HCCI Combustion Using a Stratified Hydrogen Charge

Future requirements for emission reduction from combustion engines in ground vehicles might be met by using the HCCI combustion concept. In this concept a more or less homogenous air fuel mixture is compressed to auto ignition. This gives good fuel consumption compared to a normal SI engine and its ability to burn lean mixtures at low temperatures has a positive impact on exhaust emissions. However, there are challenges associated with this concept, for instance its limited operating range and combustion control. The objective of this work is to investigate a hybrid concept, based on a combination of HCCI combustion of n-heptane and SI combustion of hydrogen. The basic idea is to initiate HCCI combustion with a spark ignited stratified lean hydrogen mixture. To verify that the combustion sequence consists of flame front combustion followed by HCCI combustion, photographs of OH chemiluminescence from the combustion were taken.
Technical Paper

Fuel equivalence ratio and EGR impact on premixed combustion rate and emission output, on a Heavy-Duty Diesel engine

This study aims to show how both NOx and soot are affected by EGR dilution when constant, as well as variations in equivalence ratio is applied together with multiple injection strategies. Experiments were conducted in a single cylinder heavy duty research engine. The effects of both EGR and equivalence ratio on partly premixed combustion were investigated. Multiple injections strategies were combined with high EGR levels and lean mixtures. Multiple injections were used to control the combustion phasing and the level of the premixed combustion rate. The diesel combustion conditioning by means of premixed combustion rate, EGR level and oxidant equivalence ratio, leads to low engine emissions. In the load range and configuration tested, emission levels below future emission standards e.g. EURO V have been shown, with no BSFC penalty or exhaust aftertreatment.
Technical Paper

HCCI Combustion Using Charge Stratification for Combustion Control

This work evaluates the effect of charge stratification on combustion phasing, rate of heat release and emissions for HCCI combustion. Engine experiments in both optical and traditional single cylinder engines were carried out with PRF50 as fuel. The amount of stratification as well as injection timing of the stratified charge was varied. It was found that a stratified charge can influence combustion phasing, increasing the stratification amount or late injection timing of the stratified charge leads to an advanced CA50 timing. The NOx emissions follows the CA50 advancement, advanced CA50 timing leads to higher NOx emissions. Correlation between CA50 can also be seen for HC and CO emissions when the injection timing was varied, late injection and thereby advanced CA50 timing leads to both lower HC and CO emissions.
Technical Paper

Modeling the Effect of Injection Schedule Change on Free Piston Engine Operation

In this study, the effects of varying the start of injection in a Free Piston Engine (FPE) have been investigated, using the KIVA-3V CFD code. In order to simulate the FPE the code has been modified by replacing the conventional crank shaft controlled piston motion by a piston motion profile calculated using a MATLAB/SIMULINK model. In this model, the piston motion is controlled by Newton's second law and the combustion process is represented by a simplified model based on ignition delay integrals and Wiebe functions. The results were tuned using predictions from the SENKIN software which are based on the detailed chemical kinetics mechanism of a Diesel oil surrogate represented by a blend of the main aliphatic (70% n-heptane) and aromatic (30% toluene) components. In order to help analyze the emission formation resulting from the HCCI/PPCI combustion modes in the engine, a special approach based on the temperature-equivalence ratio maps has been developed.
Technical Paper

Turbulence Characteristics of Tumbling Air Motion in Four-Valve S.I. Engines and their Correlation with Combustion Parameters

An experimental investigation has been carried out of the turbulence characteristics of tumble air motion in four-valve pent roof combustion chambers. This was conducted on an optically accessed single cylinder research engine under motored conditions at an engine speed of 1500 rev/min. Four cylinder heads with varying tumble magnitude were evaluated using conventional and scanning Laser Doppler Anemometry (LDA) measurements. Analysis algorithms developed to account for the effects of mean flow cyclic variations and system noise were used to obtain unbiased estimates of turbulence intensity and integral length scales. The cylinder heads were also evaluated for combustion performance on a Ricardo single cylinder Hydra engine. Mixture and EGR loops at 1500 rev/min and 1.5 bar BMEP were carried out and cylinder pressure data was analysed to derive combustion characteristics.
Technical Paper

An Experimental Investigation of Fischer-Tropsch Fuels in a Light-Duty Diesel Engine

Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.
Technical Paper

Ion Current Sensing in an Optical HCCI Engine with Negative Valve Overlap

Ion current sensors have high potential utility for obtaining feedback signals directly from the combustion chamber in internal combustion engines. This paper describes experiments performed in a single-cylinder optical engine operated in HCCI mode with negative valve overlap to explore this potential. A high-speed CCD camera was used to visualize the combustion progress in the cylinder, and the photographs obtained were compared with the ion current signals. The optical data indicate that the ions responsible for the chemiluminescence from the HCCI combustion have to be in contact with the sensing electrode for an ion current to start flowing through the measurement circuit. This also means that there will be an offset between the time at which 50% of the fuel mass has burned and 50% of the ion current peak value is reached, which is readily explained by the results presented in the paper.
Technical Paper

Reducing Pressure Fluctuations at High Loads by Means of Charge Stratification in HCCI Combustion with Negative Valve Overlap

Future demands for improvements in the fuel economy of gasoline passenger car engines will require the development and implementation of advanced combustion strategies, to replace, or combine with the conventional spark ignition strategy. One possible strategy is homogeneous charge compression ignition (HCCI) achieved using negative valve overlap (NVO). However, several issues need to be addressed before this combustion strategy can be fully implemented in a production vehicle, one being to increase the upper load limit. One constraint at high loads is the combustion becoming too rapid, leading to excessive pressure-rise rates and large pressure fluctuations (ringing), causing noise. In this work, efforts were made to reduce these pressure fluctuations by using a late injection during the later part of the compression. A more appropriate acronym than HCCI for such combustion is SCCI (Stratified Charge Compression Ignition).