Clean Low Carbon Vehicles - Combustion with Simultaneous Nitrogen and Hydrogen Enrichment

Lead Research Organisation: Brunel University
Department Name: Sch of Engineering and Design

Abstract

The project is a feasibility study of a new combustion technology that will allow an extension of the operating window of diesel engines, to include more efficient and less polluting modes through simultaneous nitrogen and hydrogen combustion enrichment. This will be achieved by on board fuel reforming and supplying of the engine with the produced oxygen-free reformate. The novelty of the system is the utilisation of the dilution effect of the reformate combined with (i) replacement of part of the hydrocarbon fuel in the engine cylinder by hydrogen, and (ii) waste heat recovery. The dilution effect is similar to that offered by the well established exhaust gas recirculation technique and by air separation membranes supplying the engine with nitrogen- enriched air in order to reduce NOx emissions. However, in the case of the proposed system the dilution effect will not be accompanied by associated drawbacks that include fuel economy, CO2 penalties and increased particulate emissions. The system will be based on the incorporation of a catalytic fuel reformer in the engine that will be fed with engine fuel (still a single fuel system) to produce the N2 and H2 containing gas mixtures. The system has the potential to lead to a clean, low CO2 emissions diesel engine that will meet emissions legislation and offer improved fuel economy. Moreover, by reducing the burden on the aftertreatment the fuel economy and CO2 emissions will be further improved.The proposed technology can be practically integrated and used in conjunction with the majority of, if not all, the proposed technologies for improving CO2 emissions of IC engine powered vehicles, and in addition to diesel engines, the potential of fuel reforming to achieve carbon reduction benefits in gasoline engines will also be evaluated.The feasibility study will be carried out in an interdisciplinary collaboration by three research groups with experience in a wide range of engine and catalysis technologies research: the Brunel University Centre for Advanced Powertrain and Fuels, the University of Birmingham Future Power Systems Group and the Cardiff University Catalysis Institute. The present project aims at proof of concept and demonstration of feasibility of the proposed engine-reformer system. The programme includes:- Study of engine combustion, performance and emissions under simulated conditions with addition of N2-H2 mixtures (Brunel). This will establish the required compositions of reformer product gas and set the target performances of the reforming process.- Catalyst studies (Cardiff) to identify stable catalysts that will selectively perform reforming reactions at relatively mild temperatures.- Study of the exhaust gas and autothermal fuel reforming processes under fully controlled reactor conditions (Birmingham) aiming at achieving the product compositions and performance targets established by the engine combustion study.- Study of engine combustion, performance and emissions with simulated reformate (Brunel). This will assess the effects of all the reformate components (such as CO) on combustion and emissions. It will also realistically evaluate the CO2 and fuel economy improvements obtained by the addition, to the engine, of gas mixtures with compositions identical to those achieved in the reactors (Birmingham) with the identified optimum catalysts (Cardiff).- Study of gasoline exhaust gas fuel reforming to evaluate how much of the energy benefit predicted from thermochemical calculations can be practically achieved (Birmingham).The outcomes of the feasibility study will provide detailed guidelines for further work to study and develop a fully integrated closed loop engine-reformer system in collaboration with automotive industrial partners. The results from the study may lead to new advances in engines with the reforming-based N2-H2 enrichment system serving as the enabling technology for developing new frontier energy saving low carbon engines.

Planned Impact

The proposed interdisciplinary research aims to lead to clean and efficient low carbon internal combustion engines. Adopting a fuel reforming system with nitrogen and hydrogen enrichment has the potential to substantially reduce CO2 and other exhaust gas emissions, thus meeting the relevant emissions legislation and contributing to the Department for Transport Carbon Reduction strategy. This will lead to societal and environmental benefits and in addition it will yield economic benefits in improved fuel efficiency. The project partners expect to generate know-how and IP relating to catalyst composition, system design, and system operation. The key stakeholders in this proposal will be the engine and vehicle OEMs and automotive catalyst manufacturers who will use the results to develop their next generation products to meet carbon reduction, fuel economy and stringent exhaust emissions targets. With public dissemination occurring throughout the project lifetime, catalyst companies, fuel producers, engine designers, and other potential end-users will be exposed to the outputs with little delay. This will enhance the probability of alternative applications being identified. It will also allow policy makers to make informed decisions based on good science. Researchers working on reformer design, combustion, emissions modelling, and IC engines will benefit from the development of this novel form of nitrogen and hydrogen enrichment that can be used to make further efficiency improvements. Greater knowledge of reforming technologies for on-board reforming will also benefit the hydrogen research as a potential interim step that can ease any transition into hydrogen economy for transportation. The project will ensure the provision of high quality training to postdoctoral researchers who will benefit from exposure to three disciplines (catalysis, combustion, reforming) and gain considerable experience of system integration. The researchers will gain knowledge and advanced skills that they can subsequently use to make a significant contribution in a research and development environment in either academia or industry.

Publications

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Description The influence of simultaneous hydrogen and nitrogen intake charge enrichment on emissions and combustion of a HSDI diesel engine was studied experimentally and the main findings include: below.

• Simultaneous NOx and smoke emissions reduction was achieved under low speed low load run. Comparison to baseline operation shows a 71.5% reduction in NOx emissions when 12% H2+N2 mixture was supplied into the engine. Under both low speed medium load and high speed low load operation considerable smoke reductions with minor changes on NOx emissions were recorded. Under high speed medium load operation the rate of NOx change appears to be very sensitive when introducing over 8% H2+N2 mixture.

• Combustion analysis: Depending on the operating conditions, NOx can be reduced, stay relatively unchanged or increased when the concentration of H2+N2 mixture is increased. Reduction of premixed combustion is accompanied with lower NOx emissions. When similar heat release curves are obtained (at two distinct H2+N2 concentrations) NOx remain relatively unchanged. Rise of premixed combustion when increasing H2+N2 fraction is accompanied with NOx increase.

• Nitrogen exhaust components: When speed or load is increased the oxidation of NO is reduced as more oxygen is consumed in the combustion process. The maximum NO2 fraction (27%) was observed at low speed low load whereas the minimum at high speed medium load operation. Raw exhaust gases contain marginal N2O and zero NH3 emissions.

• Carbon monoxide emissions: Under low load operating conditions simultaneous H2+N2 intake charge enrichment resulted in considerable CO emissions reduction. Relatively unaffected CO emissions emerged under low speed medium load run. As concerns high speed medium load operation H2+N2 addition over 4% increased CO emissions compared to baseline values.

• Brake thermal efficiency: In general H2+N2 rich intake charge has a detrimental effect on brake thermal efficiency. The engine is more fuel efficient under low speed compared to high speed operation since peak cylinder pressure occurs closer to TDC.
Exploitation Route Design of on-board hydrogen generation systems for IC engines
Sectors Energy,Transport