Development of hydrogen fuelled transport engine and field tests on vehicles

A REPORT ON

Development of hydrogen fuelled transport engine and field tests

on vehicles By: Hosam S. Rayes

Report for overview of a paper "Development of hydrogen fuelled transport engine and

field tests on vehicles " to fulfillment of the requirement the hydrogen energy system course (REE618) Department of mechanical engineering, Libyan academy

January 24, 2017

Development of hydrogen fuelled transport engine and field tests on vehicles �1

Abstract

Three wheelers have been employed as a common transport vehicle in many developing countries. The present report discusses the test results on a single cylinder typical three wheeler vehicular engine in lab and subsequent development of Hydrogen fuelled three wheelers. The report also highlights the modifications done on the test rig to ensure smooth operation without any undesirable combustion phenomena such as backfire and rapid rate of pressure rise. The engine was developed for bi-fuel operation with modifications required in the existing designs of gasoline engine to achieve hydrogen operation. Performance and exhaust emission characteristics of the engine were experimentally evaluated to meet the requirements for vehicular operation. The engine developed peak torque of 13.2 Nm@3200 rpm while operating at lean conditions. Development of fifteen hydrogen fuelled three wheelers equipped with various safety features are also discussed in the report.


Introduction

The vehicles emit their tail pipe emission closer to the ground and into densely populated regions. The rising population and economic activities have led to rise in vehicular population all over the world. The Internal Combustion Engines (ICE) which have proven to be indispensable to transport sector, are now faced with stringent emission regulations. Clean burning alternative fuels need to be adopted for operating the internal combustion engines. In this context, hydrogen is the unique fuel with the potential for providing the eventual freedom from the conditions of fuel crisis and environmental degradation.

The idea of hydrogen energy as a potential replacement to fossil fuel was formally presented at The Hydrogen Economy Miami Energy (THEME) Conference in 1975. Researchers around the world have been working towards the technological advancement in various aspects of hydrogen energy such as production, storage, transport and utilization.

Laboratory studies on hydrogen engine:

Several studies were carried out with different engine configuration and fuel induction mechanisms over the years. The experience gained from these studies led to the technical expertise to pursue several goal oriented activities in well defined direction.

Verhlest research group pin points three major issues commonly faced during hydrogen operation as:

1 lower power produced.2 NOx emission.3 backfire.


Fig. 1. Equivalence ratio suitable for hydrogen engine operation.

Hydrogen engine can be operated in ultra lean conditions where equivalence ratio could be as lean as 0.23 to stoichiometric conditions where the ER is 1. But due to unstable combustion, engines are operated at ER range of 0.4 to 1. The wide flammability of hydrogen allows ultra lean operation while the low minimum ignition energy and quenching distance could result in backfire with ER approaching stoichiometric conditions.

Table 1. shows the comparison between major properties of hydrogen and gasoline.

Compared to gasoline, hydrogen air mixture has extremely low minimum ignition energy. This property enables the conventional ignition system to be effective with a very low energy spark. On the other hand, this property makes the system susceptible surface ignition


leading to flashback, pre-ignition and rapid rates of pressure rise. Backfire can be avoided by ensuring the absence of residual combustible mixture in the intake manifold.

Fuel Induction Techniques (FIT)

The Fuel Induction Technique for a Spark Ignition engine can be classified into different categories such as Carburetion, Inlet Manifold Injection, Inlet Port Injection and Direct Cylinder Injection.

Suwanchotchoung research group reported that with continuous fuel delivery, such as with a carburetor, the incoming fuel air mixture often comes in contact with the residual hot reacting gases and causes backfire. In order to avoid backfire, it is very important to select optimum injector location and injection timing.

Varde research group studied the backfire control by late injection, which allowed hydrogen to flow into the combustion chamber only after some fresh air was let in. With electronically controlled timed injection it is possible to initiate fuel delivery late during the suction stroke.

Development of suitable injectors capable of with standing the harsh in cylinder environment with adequate life span is the major challenge in building up this system.

Fig. 2 represents the valve lift profile of the engine under present study. It also indicates the fuel injection zone adopted for the current system.

Fig. 2. Valve lift profile with injection zone representation.


Methodology

Engine system development for hydrogen operation.

The engine under study was a naturally aspirated single cylinder 396 cc gasoline engine with a carburetor. The engine was modified for bi-fuel operation (gasoline and hydrogen) considering the fact that in the event of non availability of hydrogen the vehicle can be driven on gasoline. The adjustments of operating parameters and other modifications of the vehicular engine are described below.

Compression ratio:

Compression ratio of 9.5 : 1 was selected based on the fact that the engine would be used in a three wheeler which could be powered by hydrogen as well as gasoline. Hence even though the higher octane number of hydrogen allows having higher compression ratio, it was limited to 9.5:1 to avoid knocking while running on gasoline.

Spark plug:

The spark plug used in the system was iridium instead of the usual platinum, as catalytic reaction with platinum can cause a hot spot in the combustion chamber. The spark plug gap was experimentally fixed to an optimum value of 0.4 mm. Similar observation was made by Ceper research group.

Fuel induction system:

After a series of tests using several methods of fuel induction, late timed manifold injection was adopted for the present study. The fuel injector, selected for these tests had a good flow range considering the low density of hydrogen gas. The hydrogen injection unit is shown in Fig.3.


Fig. 3. Hydrogen fuel injection system.

Lambda sensors:

The Wide Band Lambda Sensor was used instead of the conventional narrow band lambda sensors as hydrogen engine was operated at lower equivalence ratio range of under 0.6.

Electronic Control Unit (ECU):

An ECU was developed which received critical input from sensors such as the air flow sensor, engine rpm sensor, signal from cam sensor, Manifold Absolute Pressure (MAP) sensor and exhaust lambda sensor.

Flashback arrestor:

A flashback/backfire arrestor was installed in the fuel line close to the fuel injector to ensure that in the event of any backfire the flame does not travel back to hydrogen gas supply system.


Exhaust emissions:

Depending on the operating strategy used, a hydrogen engine can produce from almost zero to high concentration of NOx. NOx produced in internal combustion engines by thermal mechanism can be explained by Zeldovich mechanism. NOx formation occurs at temperatures above 1500C, and the rate of formation increases rapidly with increasing temperature. The NOx emission is considerably low at lean conditions where the equivalence ratio is in the range of 0.2 to 0.6. With increasing equivalence ratio NOx emission increases due to the higher in-cylinder temperature generated. The higher temperature is developed due to increased amount of fuel participating in combustion and also due to reduced heat absorption as the excess air is decreased with increasing equivalence ratio.

Fig. 4. Variation of NOx with equivalence ratio.


Experimental test rig

The specification of engine under study is given Table 2.

The engine speed was varied from 1200 to 3600 rpm with an increment of 400 rpm. Fig. 5 shows the variation of equivalence ratio with engine speed for hydrogen and gasoline operation.

For the carbureted gasoline operation the equivalence ratio varied from 0.84 to 1.4. The engine was operated at an equivalence ratio (Ф) in the range of 0.45 to 0.6 for operation with hydrogen. The lowest possible equivalence was chosen which could satisfy the minimum torque requirement as well as limit the NOx formation to a minimum.


As shown in Fig. 6 the engine was coupled to a dynamometer for torque measurement. Timed manifold injection was adopted as the fuel delivery strategy and late injection was adopted to avoid backfire phenomenon. The NOx emissions were measured without any after-treatment device as it exits from the exhaust manifold.


Results and discussion

As shown in Fig. 7 hydrogen operation resulted in considerable lower torque in comparison with gasoline operation especially at higher speeds. At lower speeds the hydrogen operation delivered better torque than gasoline operation.

For hydrogen operation hydrogen injectors were used and for gasoline operation the fuel was inducted by carburetion based on venturi principle. The hydrogen injector mounted between engine intake and carburetor.It was observed that at low speeds the carburetor performance was effected and the amount gasoline inducted for gasoline operation was lower leading to a lean operation with Ф = 0.84 and Ф = 0.88 at 1200 rpm and 1600 rpm respectively. Hence the power output fell in the same range at lower speeds.

The hydrogen operation resulted in flat torque curve with a maximum torque of 13.2Nm@3200 rpm where as the maximum torque was 19.5@2800 rpm for gasoline operation. This is because of the lean operation with variable equivalence ratio that has been adopted to curb the NOx emission and any backfire.


As shown in Fig. 8 the maximum power developed with hydrogen operation was 4.8 kW@ 3600 rpm compared to 6.16 kW@ 3600 rpm with gasoline operation. The lean operation coupled with volumetric efficiency drop with hydrogen operation resulted in the power drop.

Fig. 9 represents the variation of brake thermal efficiency (BTE) with engine speed for hydrogen as well as gasoline operation. The BTE with hydrogen operation is found to be higher because of lean operation strategy adopted and substantially higher energy content of hydrogen on mass basis compared to gasoline operation. The higher flame speed of hydrogen implies combustion cycle is closer to the ideal Otto cycle. The rapid energy release around top dead centre due to very high rate of burning of hydrogen-air mixtures results in higher efficiency.


Fig. 10 shows the variation of Brake Specific Fuel Consumption (BSFC) with engine speed. Due to high energy content (LHV = 120 MJ/kg) by mass, the BFSC values for hydrogen operation is substantially lower compared to gasoline operation and was in the range of 120 g/kWh. At lower speeds the BSFC was higher because of the increased time available for heat transfer and hence increased cooling loss. The BSFC was observed to be increasing at higher speed this can be attributed to increasing frictional loss in the engine.

Even though hydrogen is a carbon free fuel still it was observed that some amount of HC, CO emissions were found as shown in Figs. 11,12 and 13.


For gasoline operation the HC and CO emissions increased with engine speed. As discussed earlier, these emissions form hydrogen engines were formed due to the burning of lubricant oil. The low quenching distance of hydrogen allows the flame to travel very close to the walls and crevice volume resulting in burning of some lubricant oil present there.

Fig. 14 shows the NOx emission level of hydrogen and gasoline operation. With hydrogen operation the only major pollutant is NOx which is formed during combustion at high temperature within cylinder. The lean operation resulted in extremely low NOx emission when compared to gasoline operation. The raw NOx emission from the engine varied from 0.6 g/kWh to 5.6 g/kWh.


Development of hydrogen operated vehicle

The three wheelers are widely used by public for transport sector in India and other developing countries. This was precisely the reason for choosing such three wheelers to demonstrate their potential and utility in entering into the transport application in a number of countries. The typical hydrogen-operated three wheelers developed are shown in Fig. 15.

Compressed gas form of hydrogen storage was chosen for fuelling the vehicles. The hydrogen was stored in compressed gas form in type 3 cylinders having metal liner which is fully wrapped composite. These cylinders have been designed to withstand accident and fire hazard without releasing the contained gas. These tanks have electronically controlled solenoid valves.

Hydrogen leak detectors were mounted at multiple points, which in the event of leakage trigger an alarm and signals will be sensed by electronic control unit (ECU) which in turn immediately shuts down the engine. Besides, pressure transducers are mounted in the gas supply lines. Any leakage leads to pressure drop and prompts ECU to immobilize the vehicle by cutting the hydrogen supply. Flashback arrestors were provided before injectors to counter backfire in the event of its occurrence. The hydrogen supply lay out of the vehicle is shown below in Fig. 16.


Fig. 17 represents the various idle emissions measured from the vehicle. The measurement was made using an exhaust gas analyser with the vehicle at idling condition. The low quenching distance of hydrogen allows the flame to travel very close to the walls and crevice volume resulting in burning of some lubricant hence resulting in emission other than NOx . The only major emission was NOx and as shown in the figure it was found to be much lower compared to gasoline engine due to lean burn strategy.


ConclusionsThe single cylinder vehicular engine was optimized for hydrogen operation. Considering the present situation of low availability of hydrogen dispensing stations the vehicles were designed for bi-fuel operation. The technology has clearly shown that such a system could be ultimately adopted for total hydrogen operation once adequate amount of hydrogen would be available.A TMI-operated Hydrogen engine, under lean burn conditions has proven to be very effective in avoiding backfire and also keeping NOx emissions to a low level. The engine developed a peak power of 4.8 kW@3600 rpm, the only major emission from hydrogen engine was NOx . The NOx emission was kept below 170 ppm with hydrogen operation. The hydrogen engine developed has been successfully demonstrated in vehicle used for public transport. Such a demonstration provides first hand exposure of hydrogen as a low emission transport fuel to public.


References[1]. Development of hydrogen fuelled transport engine and field tests on vehicles/ Jayakrishnan Krishnan Unni, Premakumara Govindappa and Lalit Mohan Das / Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi 110016, India.


Development of hydrogen fuelled transport engine and field tests on vehicles

Engineering

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