Search Results

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.

Two experimental techniques, Particle Image Velocimetry (PIV) using a water-analogy Dynamic Flow Visualisation Rig (DFVR) and Laser Doppler Anemometry (LDA) in a motored research engine, were used to investigate the flow pattern generated within the combustion chamber of a gasoline direct injection (G-DI) engine. The in-cylinder flow was also modelled for the two cases using the Computational Fluid Dynamics (CFD) code VECTIS; that is, models were created using first water and then air as the working fluid. The experimental and computational results were converted into the same format and hence compared qualitatively and quantitatively. All results showed good agreement and were used to validate the different techniques. The correlation between the CFD air simulation results and the LDA results demonstrates that the CFD code can be used to predict reliably the air motion created in the combustion chamber of a G-DI 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.

This paper describes an experimental investigation to explore and optimise the performance, economy and emissions of a direct injection gasoline engine. Building on previous experimental direct injection investigations at Ricardo, a single cylinder engine has been designed to accommodate common rail electronically controlled fuel injection equipment together with appropriate port configuration and combustion chamber geometry. Experimental data is presented on the effects of chamber geometry, charge motion and fuel injection characteristics on octane requirement, lean limit, fuel consumption and exhaust emissions at typical automotive engine operating conditions. The configuration is shown to achieve stable combustion at air/fuel ratios in excess of 50:1 enabling unthrottled operation over a wide operating range. Strategies are demonstrated to control engine out emissions to levels approaching conventional port injected gasoline engines.

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.

The increasing cost of prototype engine design and development has placed new emphasis on the importance of accurate analysis of combustion chamber components. A method to assess and improve the quality of thermal boundary conditions is described. The integration of analytical approaches and experimental techniques to validate and improve thermal boundary conditions is dependent on continuous improvement of theoretical models and correlation with measured results. To monitor and improve quality, it is important to operate a closed loop of prediction, measurement and feedback to the analysis system. The development of advanced computational methods, particularly the Finite Element Method (FEM) has increased the opportunities to include detailed component thermal analysis in combustion chamber design studies. In using FEM, much emphasis is traditionally placed on “accurate” mesh generation in order to minimise element distortion and optimise element polynomial order.

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.

The spatial variation of instantaneous heat transfer in a highly rated DI diesel engine (130 mm bore, 150 mm stroke) has been investigated. Measurements have been made at key locations within the combustion chamber (valve bridge, above the piston bowl lip and bore edge) at test conditions covering the engine speed and load range. Total and radiative heat flux probes have been designed and developed to enable both the convective and radiative heat transfer components to be quantified. Transient calibration techniques have also been developed to establish the dynamic characteristics of the heat flux probes. This has removed the uncertainty normally associated with surface thermocouple diffusivity values. Considerable spatial variations in both peak and mean heat transfer have been found. The measured spatial and temporal variation in heat flux have been compared with established heat transfer models.

This paper describes latest results from the Ricardo heavy duty diesel engine research programme. Using a Diesel Kiki P-TICS II injection system, matched to a low swirl combustion chamber, emission results well within the US 1991 engineering targets have been achieved with good fuel economy. Very low NOx levels have also been demonstrated whilst maintaining good fuel economy and particulate emissions within the 1991 standards. Analysis of results indicates that injection timing and rate control, as embodied in the P-TICS approach, is a key technology for achieving these low emissions with good fuel economy.

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.

Ricardo have successfully applied their lean burn gasoline engine technology to spark ignited natural gas engines for industrial applications. An open chamber combustion system using the patented ‘Nebula’ chamber, designed as a simple conversion of a swirling direct injection diesel engine, has been tested as a part of the Ricardo internally funded research programme with very promising results. The tests with a 170 × 170 mm single cylinder research engine have shown that the Nebula gas engine provides fast combustion without excessive cyclic variation up to an air:fuel ratio of 26.5:1 or 1.67 excess air ratio. The test results achieved confirm the potential of the Ricardo Nebula combustion chamber as a lean burn combustion system. Many existing emissions standards were met with good fuel consumption, and the stringent West German and Swiss NOx limits were met at 1200 rev/min without penalties in thermal efficiency through excessive ignition retard.

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.

The use of high ratio compact combustion chambers in gasoline engines has been investigated. The objectives of the research are improved fuel economy within a given set of exhaust emission constraints. The effects of a number of parameters such as swirl, compression ratio and combustion chamber geometry have been investigated, and the conclusions are that for Europe, 13:1 compression ratio is feasible and should yield 10% better fuel economy in passenger cars, while for the USA and Japan, 11:1 compression ratio is preferable, and should yield about 5% better fuel economy.

A research programme has been carried out to investigate the effects of operating gasoline engines with different combustion systems. The results showed that at high compression ratios (13:1) compact combustion chambers allowed an increase in compression ratio of between 1 and 2½ numbers for a given fuel quality compared to conventional designs. Fuel economy benefits of about 10% could be achieved by using high ratio compact chambers and lean operation.

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.