Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Abstract

The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE's peer review process under the supervision of the session organizer. This process requires a minimum of three (3) reviews by industry experts. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. ISSN 0148-7191 Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solely responsible for the content of the paper. SAE ABSTRACTHydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO 2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NO X emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating. A combination of HCCI combustion with hydrogen fuelling has great potential for virtually zero CO 2 and NO X emissions. Nevertheless, combustion on such a fast burning fuel with wide flammability limits and high octane number implies many disadvantages, such as control of backfiring and speed of autoignition and there is almost no literature on the subject, particularly in optical engines. Experiments were conducted in a singlecylinder research engine equipped with both Port Fuel Injection (PFI) and Direct Injection (DI) systems running at 1000 RPM. Optical access to in-cylinder phenomena was enabled through an extended piston and optical crown. Combustion images were acquired by a highspeed camera at 1° or 2° crank angle resolution for a series of engine cycles. Spark-ignition tests were initially carried out to benchmark the operation of the engine with hydrogen against gasoline. DI of hydrogen after intake valve closure was found to be preferable in order to overcome problems related to backfiring and air displacement from hydrogen's low density. HCCI combustion of hydrogen was initially enabled by means of a pilot port injection of n-heptane preceding the main direct injection of hydrogen, along with intake air preheating. Sole hydrogen fuelling HCCI was finally achieved and made sustainable, even at the low compression ratio of the optical engine by means of closed-valve DI, in synergy with air-pre-heating and negative valve overlap to promote intern...

An experimental study on the effect of hydrogen enrichment on diesel fueled HCCI combustion

“…The use of hydrogen in spark ignition (SI) engines has been reviewed by Karim [9], White et al [10] and Verhelst et al [11]. It has been shown that hydrogen is an excellent fuel for satisfactory performance in SI engine applications, although there are various challenging issues [12]. Many studies have also contributed to hydrogen fueled HCCI combustion and showed that fuel efficiency obtained in a hydrogen fueled HCCI engine was significantly higher than that obtained when in a conventional diesel-fueled engine [13e18].…”

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

“…The engine used a side 6-hole injector with a stepped nozzle, typical of gasoline DI systems. The combustion imaging results indicated distorted flame shapes whose origin was thought to be related to the momentum exchange between hydrogen jetting and incylinder air-flow [4,14,42]. As far as boosted hydrogen engines are concerned, most of the published work has been done with PFI.…”

“…Stepped injector geometries are typical for multi-hole injectors for gasoline direction injection engines. Such a type of injector has been used by at University College London for optical studies of hydrogen combustion in a single-cylinder DI research engine [14]. The geometry of the holes was characterized by creating castings of the injector holes, using techniques described in [46] as shown in Figure 1, and the diameter of the outer and inner hole was measured to be 0.2 mm and 0.4 mm, respectively.…”

“…The injector had a 6-hole arrangement that consisted of two groups of 3 asymmetric holes and was mounted 45° incline on the intake side between the intake valves as shown in Figure 3. According to previous experimental work with this injector and hydrogen fuelling [4,14] it was decided to adopt the injector orientation with the two sets of plumes pointing upwards towards the pent-roof. The orientation of each injector hole was set based on angles measured from gasoline spray images previously acquired with this injector [47].…”

“…In order to eliminate hydrogen abnormal combustion modes such as pre-ignition and backfiring [8][9][10], injecting hydrogen directly into the combustion chamber (DI) after intake valves closure (IVC) has been proposed as a more suitable strategy in comparison to port fuel injection (PFI). Furthermore, closed-valve hydrogen DI eliminates issues related to air displacement from hydrogen's need of large injection durations due to its low density [11][12][13][14]. It also provides great flexibility in optimising the engine's mixture formation, performance and emission characteristics through various injection strategies, including timing and duration of injection, injection pressure, injector location and nozzle configurations [15][16][17].…”