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Experimental Results Using Ammonia Plus Hydrogen in S.I. Engine

Dr. Stefano Frigo, Department of Energy and System Engineering - University of Pisa, Italy
Prof. Roberto Gentili, Department of Energy and System Engineering - University of Pisa, Italy
Eng. Giacomo Ricci, EDI Progetti e Sviluppo , Italy

Paper Title: Experimental Results Using Ammonia Plus Hydrogen in S.I. Engine

Key words: ammonia, hydrogen, alternative fuels.

Topic group: B01 (Alternative Fuel and New Engine)

Research and/or Engineering Questions/Objective In the prospective to reduce greenhouse gas emission from vehicles, the use of hydrogen as fuel represents a possible solution. However, if proper engine running with hydrogen has been widely demonstrated, hydrogen storage onboard of the vehicle is a major problem. A solution to overcome it is to store hydrogen in the form of ammonia. The subject of this study is the possibility to fuel a S.I. internal combustion engine with ammonia plus a small percentage of hydrogen. This activity is tied to a larger-scale project, focused on an extended-range electric vehicle (EREV) that uses ammonia-plus-hydrogen for the I.C. engine and where hydrogen is obtained from ammonia by means of on-board catalytic reforming.

Methodology A two-cylinder 505 cm3 S.I. engine was adapted to ammonia-plus-hydrogen operation only modifying its intake manifold and adopting a new ECU to allow the injection of hydrogen and ammonia. Following the instrumentation of the engine and its installation on the test-bench for the experimental activity, the first tests were aimed at proving proper engine running with ammonia plus hydrogen. Then the experimental activity was focused on determining, at different engine speeds and loads, the minimum hydrogen quantity to be added to ammonia (in % by vol.) to obtain suitable engine operation. The best combination of hydrogen and ammonia to maximize engine thermal efficiency was verified as well, changing λ and engine speed and load.

Results The experimental results confirm the need of adding hydrogen in small percentage (minimum 5-6 % by volume) to ammonia to improve ignition and combustion velocity. The ratio increases decreasing engine load, showing that a minimum amount of hydrogen has always to be employed to boost engine combustion, regardless the amount of ammonia that is injected. As expected, engine cycle-to-cycle stability increases increasing hydrogen amount and, to reproduce the engine behaviour obtained with gasoline, i.e. to have the same ignition advances, roughly 40% of hydrogen has to be added to ammonia at full load and λ=1. Pre-catalyst exhaust emissions (only NOx) are low, showing a maximum value of 1700 ppm at full load and 3000 rpm.

Limitations of this study Even if, after a careful selection of the components, no meaningful inconvenience occurred during this first experimental activity, long-time reliability of the ammonia and hydrogen injection system has to be verified. Moreover, the presence of ammonia in the exhaust gas was not measured. The application of an ammonia sensor is scheduled for the next testing activity.

What does the paper offer that is new in the field including in comparison to other work by the authors? In this experimental activity a simple electronic ammonia-plus-hydrogen injection system has been implemented in a small commercial engine. The minimum amount if hydrogen, that has to be used in combination with ammonia to guarantee proper engine behaviour, was determined.

Conclusions Ammonia is an effective hydrogen carrier and can be conveniently used as fuel in internal combustion engines. However, the experimental results confirm the need of adding hydrogen to air-ammonia mixture to improve ignition and combustion velocity, with amounts that depend on engine speed and load. NOx is the only pollutant at the exhaust. This does not represent a problem anyway, since, in the case of stoichiometric mixture, the reduction achieved by a customary three-way catalyst is very effective, and, in the case of lean-burn strategy, a SCR can be easily operated since ammonia is onboard.

Session: Alternative Fuels and New Engine 2