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Future pressures to reduce the fuel consumption of passenger cars may require the exploitation of alternative combustion strategies for gasoline engines to replace, or use in combination with the conventional stoichiometric spark ignition (SSI) strategy. Possible options include homogeneous lean charge spark ignition (HLCSI), stratified charge spark ignition (SCSI) and homogeneous charge compression ignition (HCCI), all of which are intended to reduce pumping and thermal losses. In the work presented here four different combustion strategies were evaluated using the same engine: SSI, HLCSI, SCSI and HCCI. HLCSI was achieved by early injection and operating the engine lean, close to its stability limits. SCSI was achieved using the spray-guided technique with a centrally placed multi-hole injector and spark-plug. HCCI was achieved using a negative valve overlap to trap hot residuals and thus generate auto-ignition temperatures at the end of the compression stroke.

Direct gasoline injection combined with turbo charging and down sizing is a cost effective concept to meet future requirements for emission reduction as well as increased efficiency for passenger cars. It is well known that turbulence induced by in-cylinder air motion can influence efficiency. In this study, the intake-generated flow field was varied for a direct injected turbo charged concept, with the intent to evaluate if further increase in tumble potentially could lead to higher efficiency compared to the baseline. A single cylinder head with flow separating walls in the intake ports and different restriction plates was used to allow different levels of tumble to be experimentally evaluated in a single cylinder engine. The different levels of tumble were quantified by flow rig experiments.

The development of a new combustion system for a light-duty diesel engine is presented. The soot-NOx trade-off is significantly improved with maintained or improved efficiency. This is accomplished only by altering the combustion chamber geometry, and thereby the in-cylinder flow. The bowl geometry is developed in CFD and validated in single cylinder tests. Tests and simulations align remarkably well. Under identical conditions in the engine the new combustion chamber decreases smoke by 11-27%, NOx by 2-11%, and maintains efficiency as compared to the baseline geometry. The injector nozzle is matched to the new bowl using design of experiments (DoE). By this method transfer functions are obtained that can be used to optimize the system using analytical tools. The emissions show a complex dependence on the nozzle geometry. The emission dependence on nozzle geometry varies greatly over the engine operating range.

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.

This paper compares and discusses the impact of conventional and improved start strategies on the design of the exhaust aftertreatment system. It is recognised that hardware measures on the exhaust side will not be sufficient if Volvo's 5 and 6 cylinder engines are to fulfil SULEV emission levels, assuming passive three way systems only. A new start strategy, providing an excessive heat profile combined with low engine out hydrocarbon emissions, was therefore developed. Temperature profiles, raw emissions and mass flow obtained with the Lean Start Calibration will be shown for the 5 and 6 cylinder engines, both naturally aspirated as turbo. The remaining part of the paper presents a brief history of the exhaust aftertreatment design modifications for Volvo's 5 cylinder N/A engine fulfilling LEV, ULEV I, ULEV II and PZEV emission levels respectively. The impact of the new start strategy on the cold start performance will be shown.

A single-cylinder engine was operated in HCCI combustion mode with different kinds of commercial fuels. The HCCI combustion was generated by creating a negative valve overlap (early exhaust valve closing combined with late intake valve opening) thus trapping a large amount of residuals (∼ 55%). Fifteen different fuels with high octane numbers were tested six of which were primary reference fuels (PRF's) and nine were commercial fuels or reference fuels. The engine was operated at constant operational parameters (speed/load, valve timing and equivalence ratio, intake air temperature, compression ratio, etc.) changing only the fuel type while the engine was running. Changing the fuel affected the auto-ignition timing, represented by the 50% mass fraction burned location (CA50). However these changes were not consistent with the classical RON and MON numbers, which are measures of the knock resistance of the fuel. Indeed, no correlation was found between CA50 and the RON or MON numbers.

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.

Heat loss is one of the greatest energy losses in engines. More than half of the heat is lost to cooling media and exhaust losses, and they thus dominate the internal combustion engine energy balance. Complex processes affect heat loss to the cylinder walls, including gas motion, spray-wall interaction and turbulence levels. The aim of this work was to experimentally compare the heat transfer characteristics of a stepped-bowl piston geometry to a conventional re-entrant diesel bowl studied previously and here used as the baseline geometry. The stepped-bowl geometry features a low surface-to-volume ratio compared to the baseline bowl, which is considered beneficial for low heat losses. Speed, load, injection pressure, swirl level, EGR rate and air/fuel ratio (λ) were varied in a multi-cylinder light duty engine operated in conventional diesel combustion (CDC) mode.

The aim of this method is to measure emissions from components in the fuel system in a way that is comparable with regulated measurements by Sealed Housing for Evaporative Determination (SHED). In a circuit, constructed as a differential reactor, air is circulated between a test cell and a flame ionization detector (FID) for total hydrocarbon measurement. A test object, i.e. a fuel system component, is filled with fuel and placed in a sealed test cell. Due to the flow characteristic, equilibrium will occur between the air and the fuel evaporated from the surface of the test object. The amount of air consumed in the reactor is compensated by pure air being added to the system. The concentration of hydrocarbon in the circulated air is continuously measured by the FID.

A naturally aspirated in-line six-cylinder 2.9-litre Volvo engine is operated in Homogeneous Charge Compression Ignition (HCCI) mode, using camshafts with low lift and short duration generating negative valve overlap. Standard port fuel injection is used and pistons and cylinder head are unchanged from the automotive application. HCCI through negative valve overlap is recognized as one of the possible implementation strategies of HCCI closest to production. It is important to gain knowledge of the constraints and limits on the possible operating region. In this work, the emphasis is on investigating how cycle-to-cycle and cylinder-to-cylinder deviations limit the operating region, how these effects change in different parts of the operating region and how they can be controlled. At low load the cycle-to-cycle phenomena cause periodic behavior in combustion timing; together with cylinder deviations this is found responsible for decreasing the operating regime.

It is demonstrated that the cycle averaged heat flux on the hot gas side of the cylinders can be obtained using in-cylinder CFD-analysis. Together with the heat transfer coefficient obtained from the coolant jacket CFD-analysis, a complete set of boundary conditions are made available exclusively based on simulations. The engine metal temperatures could then be predicted using FEA and the results are compared to an extensive set of measured data. Also 1-D codes are used to provide cooling circuit boundary conditions and gas exchange boundary condition for the CFD-models. The predicted temperature distribution in the engine is desirable for accurate and reliable prediction of knock, durability problems, bore distortion and valve seat distortion.

The new SULEV legislation for passenger cars with gasoline powered engines, which will be introduced with the California LEV II program in the year 2003, requires a further development of the exhaust aftertreatment system. Three fundamentally different system approaches, each with very high efficiency in reducing cold start hydrocarbons, will be discussed in this paper. Vehicle test results will be presented to illustrate the potential of the respective systems towards the SULEV requirements. Durability aspects are also considered since an increased durability of 120 000 and even 150 000 miles is imposed by the legislation.

Two imaging techniques are used to investigate the interaction between developed combustion from earlier injections and partially oxidized fuel (POF) of a subsequent injection. The latter is visualized by using planar laser induced fluorescence (PLIF) of formaldehyde and poly-cyclic aromatic hydrocarbons. High speed imaging captures the natural luminescence (NL) of the prevailing combustion. Three different fuel injection strategies are studied. One strategy consists of two pilot injections, with modest separations after each, followed by single main and post injections. Both of the other two strategies have three pilots followed by single main and post injections. The separations after the second and third pilots are several times shorter than in the reference case (making them closely-coupled). The closely-coupled cases have more linear heat release rates (HRR) which lead to much lower combustion noise levels.

The objective of this investigation was to improve the thermal properties of plasma sprayed thermal barrier coatings (TBC) for internal combustion engines. There is a need for further reduction of thermal conductivity and volumetric heat capacity and the negative effects on heat loss and combustion phasing of surface roughness and permeable porosity, typical for plasma sprayed coatings, should be minimized. Four measures for improvement of TBC properties were evaluated: i) modification of the coating's microstructure by using a novel suspension plasma spraying method, ii) application of gadolinium-zirconate, a novel ceramic material with low thermal conductivity, iii) polishing of the coating to achieve low surface roughness, and iv) sealing of the porous coating surface with a polysilazane. Six coating variants with different combinations of the selected measures were applied on the piston crown and evaluated in a single cylinder light duty diesel engine.

The objective of this study was to investigate which of the artificial aging cycles available in the automotive industry that causes major deactivation of three-way catalysts (TWCs) and can be used to obtain an aged catalyst similar to the road aged converter (160 000km). Standard bench cycle (SBC) aging with secondary air injection (SAI) covered aging with various mass flows - a flow from three cylinders into one catalyst system and a flow from three cylinders into two parallel connected catalysts. For rapid catalyst bench aging, secondary air injection is a very efficient tool to create exotherms. Furthermore, the effect on catalytic activity of SAI aging with poisons from oil and fuel dopants (P, Ca, Zn) was investigated. The catalysts were thoroughly characterized in light-off and oxygen storage capacity measurements, emission conversion as a function of lambda and load variation was determined.

Thermographic phosphors thermometry was used to measure engine valves and transparent piston temperatures in two dimensions as well point wise of a running, optically accessible, gasoline direct injection engine. The engine, fueled with isooctane, was operated in continuous and skip-fire mode at 1200 and 2000 rpm. A calibration of the phosphorescence lifetime and spectral properties against temperature allowed temperature measurements between 25 and 600°C. Results from the measurements show the potential of the technique for two-dimensional mapping of engine walls, valves and piston temperatures inside the cylinder.

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.