Felix Leach

Predicting the particulate matter emissions from spray-guided gasoline direct-injection spark ignition engines

An index which links the fuel composition to particulate matter emissions (the PN index) was developed and is here evaluated with model fuels in a single-cylinder optical-access spray-guided direct-injection engine; the model fuels have independent control of the double-bond content and volatility, as used in the index. This index is investigated in three different engines: a single-cylinder research engine, a V8 engine recently available in the market and a current-production supercharged V6 engine. A number of market gasolines were tested in all three engines, and the results follow the trends predicted by the particle number index. Imaging of the in-cylinder sprays shows that the composition of the model fuels affects the mixture homogeneity and their particulate matter emissions; in particular, the lack of a light end in the model fuel composition can lead to misleadingly low particle number emissions owing to improved mixture preparation which is unrepresentative of market fuels. The PN index was investigated in a Jaguar Land Rover V6 engine with five different fuels over a simulated New European Driving Cycle, and the results show that the index trends are followed. The emissions were evaluated from two fuels representing the EU5 reference-fuel specifications that has been developed using the particle number index to give a difference in particulate matter emissions. The results from these fuels show that a difference in the particle number emissions of a factor of about 2 can be seen at both stoichiometric conditions and rich conditions, for two fuels representative of the EU5 reference-fuel specifications. This follows trends predicted by the particle number index. This has important implications for policy makers and European Union legislation, where particle number emissions from gasoline vehicles are now regulated for the first time, as batch-to-batch variations in the fuel composition would result in different test results under the current legislation.

Alcohol fuels for spark-ignition engines : performance, efficiency and emission effects at mid to high blend rates for binary mixtures and pure components

The paper evaluates the results of tests performed using mid- and high-level blends of the low-carbon alcohols, methanol and ethanol, in admixture with gasoline, conducted in a variety of test engines to investigate octane response, efficiency and exhaust emissions, including those for particulate matter. In addition, pure alcohols are tested in two of the engines, to show the maximum response that can be expected in terms of knock limit and efficiency as a result of the beneficial properties of the two alcohols investigated. All of the test work has been conducted with blending of the alcohols and gasoline taking place outside the combustion system, that is, the two components are mixed homogeneously before introduction to the fuel system, and so the results represent what would happen if the alcohols were introduced into the fuel pool through a conventional single-fuel-pump (dispenser) approach. While much has been written on the effect of blending the light alcohols with gasoline in this way, the results present significant new findings with regard to the effect of the enthalpy of vaporization of the alcohols in terms of particulate exhaust emissions. Also, in one of the tests, two mid-level blends are tested in a highly downsized prototype engine – these blends being matched for stoichiometry, enthalpy of vaporization and volumetric energy content. The consequences of this are discussed and the results show that this approach to blend formulation creates fuels which behave in the same manner in a given combustion system; the reasons for this are discussed. One set of tests using pure methanol alternately with cooled exhaust gas recirculation and with excess air shows a significant increase in thermal efficiency that can be expected as the blend level is increased. The effect on nitrous oxide emissions is shown to be similarly beneficial, this being primarily a result of the enthalpy of vaporization of the alcohol cooling the charge coupled with the lower adiabatic flame temperature of the alcohol. Whereas it is normally a beneficial characteristic in spark-ignition combustion systems, one disadvantage of a high value of enthalpy of vaporization is shown in another series of tests in that, in admixture with gasoline, it is a driver on flash boiling of the hydrocarbon component in the blend in direct injection combustion systems. In turn, this causes the particulate emissions of the engine to increase quite markedly over those of ethanol–gasoline blends at the same stoichiometry. The paper shows for the first time the dichotomy of the potential efficiency improvement with the challenge of particulate control. This effect poses a challenge for the future introduction and use of such high blend rate fuels in engines without particulate filters. Although it must be stated that the overall particulate emissions of the methanol–gasoline blend are lower than for gasoline, the effect is only present at extremely low load, and that there is a likelihood that particulate filters will be adopted in production vehicle anyway, nullifying this issue.

Particulate emissions from a highly boosted gasoline direct injection engine

Downsized, highly boosted, gasoline direct injection engines are becoming the preferred gasoline engine technology to ensure that increasingly stringent fuel economy and emissions legislation are met. The Ultraboost project engine is a 2.0-L in-line four-cylinder prototype engine, designed to have the same performance as a 5.0-L V8 naturally aspirated engine but with reduced fuel consumption. It is important to examine particle number emissions from such extremely highly boosted engines to ensure that they are capable of meeting current and future emissions legislation. The effect of such high boosting on particle number emissions is reported in this article for a variety of operating points and engine operating parameters. The effect of engine load, air–fuel ratio, fuel injection pressure, fuel injection timing, ignition timing, inlet air temperature, exhaust gas recirculation level, and exhaust back pressure has been investigated. It is shown that particle number emissions increase with increase in cooled, external exhaust gas recirculation and engine load, and decrease with increase in fuel injection pressure and inlet air temperature. Particle number emissions are shown to fall with increased exhaust back pressure, a key parameter for highly boosted engines. The effects of these parameters on the particle size distributions from the engine have also been evaluated. Significant changes to the particle size spectrum emitted from the engine are seen depending on the engine operating point. Operating points with a bias towards very small particle sizes were noted.

Evaluation of exhaust gas recirculation techniques on a high-speed direct injection diesel engine using first law analysis:

The effects of different exhaust gas recirculation (EGR) strategies on engine efficiency and the resulting energy flows at two speed/load conditions (1500 r/min/6.8 bar net indicated mean effective pressure (nIMEP) and 1750 r/min/13.5 bar nIMEP) were studied using a first law analysis approach. The EGR strategies tested were as follows: cooled high-pressure exhaust gas recirculation (baseline), the application of exhaust gas recirculation with the swirl flap closed and the use of exhaust gas recirculation under constant λ conditions. The closed swirl flap exhaust gas recirculation strategy reduced brake efficiency under high load conditions and increased heat transfer to the coolant for both load cases. Soot and CO emissions increased at high load, however, with an increase in NOx relative to the baseline case. The constant λ exhaust gas recirculation strategy reduced brake efficiency under low load, as well as the heat flow to the coolant for both load cases. The constant λ exhaust gas recirculation strategy benefited smoke emissions and increased combustion exhaust gas recirculation tolerance, albeit with a penalty in NOx emission.

Particulate matter emissions from gasoline direct injection spark ignition engines

ABSTRACT An index, linking fuel composition with Particulate Matter (PM) emissions (PN index) has been developed and here is evaluated with model fuels in a single cylinder, optical access, Spray Guided Direct Injection (SGDI) engine. Imaging of in-cylinder evaporation shows the composition of model fuels affects their PM emissions. Emissions are evaluated from two fuels representing the EU5 reference-fuel specification, developed using the PN index to give a difference in PM emissions, showing a 40% variation. The index is investigated in a Jaguar V6 engine with five different fuels over a simulated NEDC. The results show the index trends are followed.

A New Method for Measuring Fuel Flow in an Individual Injection in Real Time

Knowledge of fuel mass injected in an individual cycle is important for engine performance and modeling. At the moment, such measurements are not possible on engine or in real time. In this article, a new method using Coriolis flow meters (CFMs) and a new, patented, signal processing technique, known as the Prism, are introduced. CFMs are extensively used for flow measurement both in the automotive industry and further afield and, when coupled with the Prism, have the potential to make these challenging high-speed measurements. A rig-based feasibility study was conducted injecting very small quantities of diesel (3 mg) at pressures of up to 1000 bar at simulated engine speeds of up to 4000 rpm. The results show that these small quantities can in principle be measured. The results also reveal a previously unknown behavior of CFMs when measuring very low flow rates at high speed. The study concludes that by combining high-resonant frequency flow tubes with the Prism technology in a new instrument—the fast next-generation Coriolis (fast NGC) flow meter—it will be possible to measure individual injector flow rates on engine in real time.

Effect of Thermocouple Size on the Measurement of Exhaust Gas Temperature in Internal Combustion Engines

Accurate measurement of exhaust gas temperature in internal combustion engines is essential for a wide variety of monitoring and design purposes. Typically these measurements are made with thermocouples, which may vary in size from 0.05 mm (for fast response applications) to a few millimetres. In this work, the exhaust of a single cylinder diesel engine has been instrumented both with a fast-response probe (comprising of a 50.8 μm, 127 μm and a 254 μm thermocouple) and a standard 3 mm sheathed thermocouple in order to assess the performance of these sensors at two speed/load conditions. The experimental results show that the measured time-average exhaust temperature is dependent on the sensor size, with the smaller thermocouples indicating a lower average temperature for both speed/load conditions. Subject to operating conditions, measurement discrepancies of up to ~80 K have been observed between the different thermocouples used. Thermocouple modelling supports the experimental trends and shows that the effect of conduction is inversely proportional to the thermocouple junction size-an effect attributed to changes in the thermal inertia of the device. This conduction error is not typically considered in the literature for exhaust gas temperature measurement. Modelling results also show that radiative heat transfer is small compared to the effect of conduction on the measurements. Finally, a new dynamic response thermocouple compensation method is presented, in order to correct for the dynamic error induced by the thermocouples. This technique recovers the “true” gas temperature with a maximum error of ~1.5-2% in peak temperature depending on speed/load conditions.

An optical method for measuring exhaust gas pressure from an internal combustion engine at high speed

Measurement of exhaust gas pressure at high speed in an engine is important for engine efficiency, computational fluid dynamics analysis, and turbocharger matching. Currently used piezoresistive sensors are bulky, require cooling, and have limited lifetimes. A new sensor system uses an interferometric technique to measure pressure by measuring the size of an optical cavity, which varies with pressure due to movement of a diaphragm. This pressure measurement system has been used in gas turbine engines where the temperatures and pressures have no significant transients but has never been applied to an internal combustion engine before, an environment where both temperature and pressure can change rapidly. This sensor has been compared with a piezoresistive sensor representing the current state-of-the-art at three engine operating points corresponding to both light load and full load. The results show that the new sensor can match the measurements from the piezoresistive sensor except when there are fast temperature swings, so the latter part of the pressure during exhaust blowdown is only tracked with an offset. A modified sensor designed to compensate for these temperature effects is also tested. The new sensor has shown significant potential as a compact, durable sensor, which does not require external cooling.