Miroslaw L. Wyszynski

On-board generation of hydrogen-rich gaseous fuels: a review

Abstract Hydrogen has a good potential as an alternative fuel for spark ignition engines. It can extend the lean flammability limit of conventional fuels in order to achieve higher thermal efficiency and lower exhaust emissions. This paper reviews the use of hydrogen and hydrogen-enriched gasoline as a fuel for SI engines and the techniques used to generate hydrogen from liquid fuels such as gasoline and methanol, on-board the vehicle. The processes of thermal decomposition, steam reforming, partial oxidation and exhaust gas reforming are evaluated. A considerable amount of both theoretical and experimental work has been done in this field. Predictive and experimental results of the various investigators are reviewed and summarized.

HYDROGEN ENRICHMENT: A WAY TO MAINTAIN COMBUSTION STABILITY IN A NATURAL GAS FUELLED ENGINE WITH EXHAUST GAS RECIRCULATION, THE POTENTIAL OF FUEL REFORMING

Abstract An experimental study was carried out to evaluate the potential of hydrogen enrichment to increase the tolerance of a stoichiometrically fuelled natural gas engine to high levels of dilution by exhaust gas recirculation (EGR). This provides significant gains in terms of exhaust emissions without the rapid reduction in combustion stability typically seen when applying EGR to a methane-fuelled engine. Presented results give the envelope of benefits from hydrogen enrichment. In parallel, the performance of a catalytic exhaust gas reforming reactor was investigated in order that it could be used as an onboard source of hydrogen-rich EGR. It was shown that sufficient hydrogen was generated with currently available prototype catalysts to allow the engine, at the operating points considered, to tolerate up to 25 per cent EGR, while maintaining a coefficient of variability of indicated mean effective pressure below 5 per cent. This level of EGR gives a reduction in NO emissions greater than 80 per cent in all test cases.

Effect of hydrogen addition on natural gas HCCI combustion

Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve HCCI (homogeneous charge compression ignition) engine operation. Previous work by the authors has shown that hydrogen addition improves combustion stability in various difficult combustion conditions. It is shown here that hydrogen, together with residual gas trapping, helps also in lowering the intake temperature required for HCCI. It has been argued in literature that the addition of hydrogen advances the start of combustion in the cylinder. This would translate into the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke. The experimental results of this work show that, with hydrogen replacing part of the fuel, a decrease in intake air temperature requirement is observed for a range of engine loads, with larger reductions in temperature noted at lower loads. It is also shown that the low NOx emissions and high rates of heat release, typical for HCCI, are retained with hydrogen-assisted operation, especially at low engine loads. A practical possibility of producing the necessary hydrogen in a fuel reformer fitted in the exhaust gas recirculation system is illustrated for one engine condition.

Exhaust gas reforming of gasoline at moderate temperatures

Abstract This paper presents theoretical and experimental results of exhaust gas reforming of gasoline at lower reformer temperatures (650 and 600 °C). The reformed fuel, containing some quantities of hydrogen and carbon monoxide, was fed at a constant rate to the intake manifold of a single cylinder Ricardo E6 engine as an additive to gasoline. The study of the effects of reformed gas addition on engine performance at extreme lean burn conditions was performed at fixed conditions of speed, load and throttle setting, for different ignition timing settings. Results are encouraging in terms of improved engine efficiency and extended lean burn operation for most ignition timings, despite quite low hydrogen content in the reformed fuel which resulted in low proportions of energy input to the engine from the reformed fuel. Also the levels of pollutant exhaust contents (NO x and HC) were lower and cycle-to-cycle variations of cylinder pressure were reduced.

The pressure swing adsorption drying of compressed air

Abstract An experimental and theoretical study of the drying of compressed air by a granular silica gel adsorbent was carried out using pressure swing adsorptio This process uses a portion of the dried air expanded to a lower pressure to purge the saturated bed for regeneration purposes. The effect of the volum ratio purge flow/feed flow on the dry air humidity when the process has reached quasi-steady state was investigated over the range 0.85–1.48. These humidities were predicted successfully by a simplified dynamic adsorption model using previously determined equilibrium and rate data. The approach to this steady state was also predicted. The calculated values of the humidity of the outlet regeneration flow indicate the potential of this process for the enrichment of trace adsorbates.

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine Philip Price , Richard Stone Jacek Misztal, Hongming Xu, Miroslaw Wyszynski, Trevor Wilson and Jun Qiao Department of Engineering Science, University of Oxford, OX1 3PJ, UK Department of Mechanical Engineering, University of Birmingham, B15 2TT, UK Jaguar Research, Whitley Engineering Centre, CV3 4LF, UK philip.price@eng.ox.ac.uk

Research on expansion of operating windows of controlled homogeneous auto-ignition engines

Abstract A major effort has been made to surmount the current obstacles to expanding the operating window of homogeneous charge compression ignition (HCCI) engines. The research involves extensive experimental studies on single-cylinder and multi-cylinder engines and the work is devoted to the development of on-board fuel-reforming technology and to the application of supercharging combined with trapping of residual gases in the cylinder. Fuel reforming yields significant quantities of hydrogen and is used to extend the lower load boundary while supercharging and internal exhaust gas recirculation (EGR) trapping are used to increase the upper load limit of HCCI engines. The present paper highlights the main findings of the research to date; in particular it reveals that using a combination of technical elements for effective control of auto-ignition in a typical passenger car engine configuration is possible and promising.

Effect of inlet valve timing on boosted gasoline HCCI with residual gas trapping

With boosted HCCI operation on gasoline using residual gas trapping, the amount of residuals was found to be of importance in determining the boundaries of stable combustion at various boost pressures. This paper represents a development of this approach by concentrating on the effects of inlet valve events on the parameters of boosted HCCI combustion with residual gas trapping. It was found that an optimum inlet valve timing could be found in order to minimize NOx emissions. When the valve timing is significantly advanced or retarded away from this optimum, NOx emissions increase due to the richer air / fuel ratios required for stable combustion. These richer conditions are necessary as a result of either the trapped residual gases becoming cooled in early backflow or because of lowering of the effective compression ratio. The paper also examines the feasibility of using inlet valve timing as a method of controlling the combustion phasing for boosted HCCI with residual gas trapping.

AN EXPERIMENTAL STUDY OF BIOETHANOL HCCI

ABSTRACT Bioethanol has been successfully used in conventional spark ignition (SI) internal combustion engines. Homogeneous charge compression ignition (HCCI) combustion, a novel combustion method, has shown the potential for low nitric oxides (NOx) emissions with no particulate matter formation. This paper explores two different approaches to achieve HCCI with bioethanol; namely, trapping of internal residual gas and intake temperature heating with a high compression ratio. For naturally aspirated HCCI operation with residual gas trapping on a spark ignition engine, although the NOx emissions were low, the load range was unacceptably small. When inlet manifold pressurisation was employed, a substantial increase in the upper load boundary could be achieved without any substantial increase in NOx emissions. With forced induction, the feasibility of using boost control as the main method of load control for higher engine loads during HCCI operation has been explored with possible methods of utilizing boost control. One possible strategy is a map based strategy where fuelling rates are correlated versus boost pressure and trapped residual amounts. A proof of concept using this strategy showed that transient operation from a low load to a much higher load, using boost control might be possible without engine misfire.

HCCI Engine Modeling for Real-Time Implementation and Control Development

A propane-fueled homogeneous charge compression ignition (HCCI) engine model has been developed for the development of new engine control strategies in which a single-zone combustion mathematical model is adopted. The model has a reasonably simple structure and is implemented in a SIMULINK environment for simulation studies. The results of simulation studies show that the model can provide information on autoignition timing, engine work output, gas temperature, and concentrations of in-cylinder species. Model validation has been conducted by comparing the simulated output with experimental results obtained from a single-cylinder HCCI research engine. The comparison shows a fair agreement between the simulation and experimental results.