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A single cylinder, naturally aspirated, four-stroke and camless gasoline engine was operated in gasoline compression ignition mode or otherwise known as homogeneous charge compression ignition (HCCI) mode. The valve timing could be adjusted during engine operation, which made it possible to operate the engine on HCCI combustion in the part-load regime of a 5-cylinder 2.4 liter engine. Cycle to cycle variation in cylinder pressure is caused by the shifts in the auto-ignition timing of the air-fuel mixture. These variations during HCCI combustion were found to, be predictable to some extent, in the sense that an early phased combustion follows a later phased one and vice versa. When the engine was operated in spark ignition mode, a late combustion was correlated with a high gas temperature. No such correlation was found when the engine was operated in HCCI mode.

Heat transfer to the walls of the combustion chamber is increased by engine knock. In this study the influence of knock onset and knock intensity on the heat flux is investigated by examining over 10 000 individual engine cycles with a varying degree of knock. The heat transfer to the walls was estimated by measuring the combustion chamber wall temperature in an SI engine under knocking conditions. The influence of the air-fuel ratio and the orientation of the oscillating cylinder pressure-relative to the combustion chamber wall-were also investigated. It was found that knock intensities above 0.2 Mpa influenced the heat flux. At knock intensities above 0.6 Mpa, the peak heat flux was 2.5 times higher than for a non-knocking cycle. The direction of the oscillations did not affect the heat transfer.

SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions-releasing moderate amounts of heat-transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas-by low temperature chemistry-between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modeling of the end-gas reactions.

Operating an engine in homogeneous charge compression ignition (HCCI) mode requires the air fuel mixture to be very lean or highly diluted with residuals. This is in order to slow the kinetics down and to avoid too rapid heat release. Consequently, the operational window for the engine in HCCI mode is not the same as for the engine operating in spark ignited (SI) mode. Homogeneous charge compression ignition engine mode, in this study, is accomplished by trapping residual mass using variable valve timing. With the residual trapping method, the engine cannot be started in HCCI mode and due to the dilution, the engine in HCCI mode can only be operated in the part - load regime. Hence, a mode change between spark ignited and HCCI modes, and vice versa is required. This study reports the development of a mode change strategy for a single cylinder camless engine, and its successful implementation in a camless multi cylinder engine.

In a diesel engine, the combustion and emissions formation are governed by the spray formation and mixing processes. To meet the stringent emission legislations of the future, which will demand substantial reductions of NOX and particulate emissions from diesel engines, the spray and mixing processes play a major roll. Different fuel injection systems and injection strategies have been developed to achieve better performance and lower emissions from the diesel engine almost without investigating the influence of the injector nozzle orifices. A reduction in the nozzle orifice diameter is important for an increased mixing rate and formation of smaller droplets which is beneficial from emissions and fuel consumption point of view, as long as the local air-to-fuel ratio (AFR) is kept at a sufficiently lean level.

Projected stringent emissions legislation will make tough demands on engine development. For diesel engines, in which combustion and emissions formation are governed by the spray formation and mixing processes, fuel injection plays a major role in the future development of cleaner engines. It is therefore important to study the fundamental features of the fuel injection process. In an engine the fuel is injected at high pressure into a pressurized and hot environment of air, which causes droplet formation and fuel evaporation. The injected fuel then forms a gaseous phase surrounding the liquid phase. The amount of evaporated fuel in relation to the total amount of injected fuel is of importance for engine performance, i.e. ignition delay and mixing rate. In this paper, the fraction of evaporated fuel was determined for sprays, using different orifice diameters ranging from 0.100 mm up to 0.227 mm, with the aid of a high-pressure spray chamber.

This paper presents a follow on study from earlier work investigating the influence of fuel parameters on the deposit formation and emissions from a direct injection stratified charge spark ignition engine. It was shown that injector fouling was the main reason for the increase in unburned hydrocarbon emissions and spray visualizations supported these results. The hypothesis is that the deposit buildup in the injector caused the increased hydrocarbon emissions due to an increased wall film formation. To further verify the findings, Phase Doppler Anemometry measurements at simulated engine conditions, were performed. Measurements recorded on the injector axis 20 mm downstream from the injector orifice, showed that the initial pre-jet velocity was 30% higher and the drop mean diameter was 5% larger in the case of a used injector compared to a new injector. Based on these investigations, spray files were set-up in the 3-D CFD-code AVL FIRE™.

The effects of injection pressure and duration on exhaust gas emissions, sooting flame temperature, and soot distribution for a heavy–duty single cylinder DI diesel engine were investigated experimentally. The experimental analysis included use of two–color pyrometry as well as “conventional” measuring techniques. Optical access into the engine was obtained through an endoscope mounted in the cylinder head. The sooting flame temperature and soot distribution were evaluated from the flame images using the AVL VisioScope™ system. The results show that the NOx/soot trade–off curves could be improved by increasing injection pressure. An additional reduction could also be obtained if, for the same level of injection pressure, the injection duration was prolonged.

An engine with variable valve timing was operated in homogeneous charge compression ignition (HCCI) mode. In two sets of experiments, the fuel was introduced directly into the combustion chamber using a split injection strategy. In the first set, lambda was varied while the fuel flow was constant. The second set consisted of experiments during which the fuel flow was altered and lambda was fixed. The results were evaluated using an engine simulation code with integrated detailed-chemistry. The auto-ignition temperature of the air-fuel mixture was reached when residual mass of the previous combustion cycle was captured using a negative valve overlap and compressed together with the fresh mixture charge inducted. When a pilot fuel amount was introduced in the combustion chamber before piston TDC, during the negative valve overlap, radicals were formed as well as intermediates and combustion took place during this overlap provided the mixture was lean.

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.

Reducing emissions and improving efficiency are major goals of modern internal combustion engine research. The use of biomass-derived fuels in Diesel engines is an effective way of reducing well-to-wheels (WTW) greenhouse gas (GHG) emissions. Moreover, partially premixed combustion (PPC) makes it possible to achieve very efficient combustion with low emissions of soot and NOx. The objective of this study was to investigate the effect of using alcohol/Diesel blends or neat alcohols on emissions and thermal efficiency during PPC. Four alcohols were evaluated: n-butanol, isobutanol, n-octanol, and 2-ethylhexanol. The alcohols were blended with fossil Diesel fuel to produce mixtures with low cetane numbers (26-36) suitable for PPC. The blends were then tested in a single cylinder light duty (LD) engine. To optimize combustion, the exhaust gas recirculation (EGR) level, lambda, and injection strategy were tuned.

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.

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.

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.

When using dimethyl ether (DME) to fuel diesel engines at high load and speed, applying high amounts of exhaust gas recirculation (EGR) to limit NOX emissions, carbon monoxide (CO) emissions are generally high. To address this issue, the combustion and emission processes in such engines were analyzed with the three-dimensional CFD KIVA3V code. The combustion sub-mechanism (76 species and 375 reactions) was validated by comparing simulated ignition delays and flame velocities to reference data under diesel-like and atmospheric conditions, respectively. In addition, simulated and experimentally determined rate of heat release (RoHR) curves and emission data were compared for a heavy-duty single-cylinder DME engine (displaced volume, 2.02 liters) with DME-adapted piston and nozzle geometries. The simulated RoHR curves captured the main features of the experimentally measured curves, but deviated in the premixed (higher peak) and late combustion phases (too high).

The possibilities for extending the range of engine loads in which soot and NOx emissions can be minimised by using low temperature combustion in conjunction with high levels of EGR was investigated in a series of experiments with a single cylinder research engine. The results show that very low levels of both soot and NOx emissions can be achieved at engine loads up to 50 % by reducing the compression ratio to 14 and applying high levels of EGR (up to approximately 60 %). Unfortunately, the low temperature combustion is accompanied by increases in fuel consumption and emissions of both HC and CO. However, these drawbacks can be reduced by advancing the injection timing. The research engine was a 2 litre direct injected (DI), supercharged, heavy duty, single cylinder diesel engine with a geometry based on Volvo's 12 litre engine, and the amount of EGR was increased by adjusting the exhaust back pressure while keeping the charge air pressure constant.

One of the problems encountered when operating Diesel engines in HCCI mode is a too early start of combustion, due to the low ignition resistance of Diesel fuels. Correct phasing of the combustion process requires a lower in-cylinder temperature during compression. One possibility of regulating the temperature is to adjust the intake valve closing timing and thus the effective compression ratio. A single cylinder research engine, configured as a passenger car type DI Common Rail Diesel engine, was fitted with a fully adjustable hydraulic valve train, which allowed free settings of the valve timing events. Premixed combustion was achieved by injecting the fuel during the compression stroke, prior to ignition, in multiple steps. Different combinations of intake valve closing timing and external EGR were tested as well as the possibility to use internal EGR for combustion control.

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.

During 1990, the Volvo Car Corporation will Introduce a new In-line six-cylinder engine featuring three litre displacement, twin overhead camshafts and 24 valves, designated the B6304F. The engine has been designed and adapted for Volvo's top-of-the-line model 960, and it has been developed to meet the market's high demands on comfort, performance, reliability, economy and environmental friendliness. The engine has been designed and manufactured with the help of advanced CAE technology. The engine structure consists of five basic aluminium parts. This construction contributes to the low engine weight of 182 kg including auxiliary units, oil and wiring. The engine's gas flow has been optimized with the help of data simulation and laser measurement technology so as to ensure efficient utilization of energy. Fuel injection and ignition timing are regulated and controlled by an advanced electronic control system, the Bosch Motronic 1.8.

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.