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Future emissions standards (TIER II, LEV2) require that diesel fuelled vehicles meet the same emissions levels as their gasoline counterparts. In addition, Sport Utility Vehicles (SUVs) must comply to the same norms as passenger cars. However the diesel engine has many desirable attributes for SUV applications and an important role to play in addressing fuel consumption and CO2 emissions issues. In-cylinder reduction of pollutants can no longer be relied upon as the major means to meet future standards. Solutions based solely on emissions control technology are also unlikely to yield positive results. The only viable solution is the combined use of in-cylinder emissions control with advanced catalyst technologies. However, a highly integrated approach is required to gain maximum benefit from the technologies used and enable very low targets to be achieved.

It is expected that heavy duty engine legislation in Europe will continue to drive down test cycle BSNox emissions to levels of between 2.5 and 3.5 g/kWh by 2005, with a reduction in particulate emissions to between 0.02 and 0.08 g/kWh. It is unlikely that re-optimisation of existing engine combustion systems alone, such as further retardation of the fuel injection timing, will be sufficient to meet the legislated BSNox targets. Other measures, such as cooled EGR or new aftertreatment systems must therefore be considered. Such emissions control strategies may conflict with other market requirements for improved fuel consumption and increased power density. In this paper, research at Ricardo into the configuration of a premium heavy duty truck engine for the European market for model year 2005 and beyond, is described. A review of the market requirements, projected to 2005 was undertaken in order to define the specification of the concept engine.

Using an engine simulation code (WAVE) combined with statistical experimental design and optimisation techniques, the potential of a combined Miller cycle and internal EGR heavy duty engine for future truck applications (Euro 3 and 4) has been assessed. The practical issues related to a suitable variable valve timing or actuation system and boosting strategy have been considered. It is found that, whilst internal EGR levels suitable for future European emissions legislation cycles are possible, the boost pressures needed at high load to maintain a suitable air/fuel ratio when running a valve timing strategy to give acceptable levels of in-cylinder temperature (via the Miller system) are beyond the capabilities of current technology. It is believed, however, that such a system may still be suitable for application in markets which have duty cycles less dependent upon full load operation, for example Japan and, possibly, the USA.

The methods of operation of four of the leading combustion system designs for fuel only gasoline direct injection (G-DI) engines have been compared by applying a classical analysis procedure for defining fuel transport. The fuel spray requirements for the different systems are discussed in relation to results obtained from a Phase Doppler Anemometry (PDA) rig for different injectors. The combustion systems have then been considered regarding the functional requirements of future G-DI engines. These include power potential, stratified and homogeneous performance, variable air motion requirements, OEID component function monitoring, packaging and manufacturing issues and calibration effort. The paper concludes that there are at least four main approaches capable of producing acceptable combustion and that the choice of system will depend on packaging, cost and manufacturing constraints.

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.

Twenty-three hydrocarbon components were analysed in the exhaust emissions from a 2.3 litre gasoline engine. The effect of a three-way catalyst on emission rates was investigated, as was the effect of addition to fuel of specific aromatic and olefinic compounds. The addition of 1-hexene and 1-octene (olefins) caused statistically significant increases in reactive olefins - ethene and propene - in the exhaust. The addition of benzene and toluene led to increases in these compounds in the exhaust, and indicated that whilst fuel-toluene is the main source of toluene emissions, the emission of benzene has sources in addition to fuel-benzene. A three-way catalyst, when operating at > 600°C, eliminated most hydrocarbons except methane and traces of the light aromatics. At idle, however, the catalyst exhibited substantial selectivity towards different hydrocarbons according to their ease-of-oxidation.

Gaseous emissions were sampled from the exhaust of a single cylinder version of a modern four-valve homogeneous charge spark-ignition engine. The hydrocarbon emissions were extensively analysed using capillary gas chromatography. Levels of key components of the hydrocarbons including methane, benzene and 1, 3-butadiene, were related to fuel composition, mixture strength and exhaust gas recirculation rate. It was shown that the relative levels of hydrocarbon emissions could generally be explained from a knowledge of chemical mechanisms. The significance of the observed trends for the development of engines with reduced levels of hydrocarbon emissions is considered.

Natural gas is one of the alternative fuels to diesel being considered for low emissions heavy-duty applications. The favoured operating strategies for low emissions SI gas engines are identified as those with high levels of dilution - stoichiometric operation with EGR, and lean-burn. A well-matched exhaust catalyst is needed to produce the lowest emissions levels. Increasing the accuracy of transient air-fuel ratio control is shown to improve the emissions still further. The most favourable combinations of engine operating strategy and control accuracy are identified with respect to fuel economy and first cost. The Co-Nordic Natural Gas Bus Project is an example of an engine development programme aimed at achieving the lowest possible exhaust emissions levels, and as such uses the lowest emissions approach of a stoichiometric engine strategy with EGR and high accuracy control.

The advantages of closed, loop over open loop control systems are generally recognised. However, existing engine management systems implement most control functions in open loop because suitable feedback sensors are not available. Even for so-called closed loop air fuel ratio controllers, shortcomings of the exhaust gas oxygen (EGO) sensor limit the potential effectiveness of closed loop control. A more direct measure of the combustion process, such as cylinder pressure, can yield sufficient information for the closed loop operation of many of the combustion control functions; this paper presents the results of a prediction algorithm which can derive a variety of feedback signals from cylinder pressure. Cylinder pressure, together with several combustion variables, including air-fuel ratio, exhaust gas recirculation rate, and NOx HC, CO and CO2 emissions were measured at various operating points.

It has been shown by calculation that, for given engine operating conditions, there should be an optimum rate of combustion for minimum Nox emissions from spark ignited engines. This paper gives experimental results from a single cylinder engine which confirm the theory, and show that, for a particular engine, the normal combustion rate needed reducing at zero EGR and increasing at high EGR rates, in opposition to its natural tendency to decrease. The effect on economy was a small loss at zero EGR, but an appreciable improvement at high EGR. Cyclic variation and octane requirement studies are also included.