Section
15 Engines supplied with low pressure gas
15.1 General
15.1.2 The requirements apply to engines in which gas is introduced either into
the air inlet manifold, scavenge space or cylinder air inlet channel port or mixed
with air before the turbocharger (‘pre-mixed engines’) and the gas/air mixture in
the cylinder is ignited by the combustion of a certain amount of fuel (pilot
injection) or by extraneous ignition (sparking plug).
15.1.3 The requirements apply to, but are not limited to, engines for mechanical propulsion
and generating sets intended for main propulsion and auxiliary applications in
single engine or multi-engine installations.
15.1.4 In addition to the requirements described in this Chapter, the requirements relating
to engines in the following Rule sets are also to be satisfied:
15.1.5 For DF and GF engines, the maximum power available in gas mode and the
corresponding conditions shall be stated by the engine manufacturer and demonstrated
during the type test. The gas methane number during the test is to be recorded. The
test should be performed with the minimum methane number acceptable by the engine
without leading to engine derating. Type testing requirements are given in LR’s Type Approval System Test Specification Number
4.
15.2 Submission requirements
15.2.1 The plans and particulars are to be submitted as required in Table 2.15.1 Plans and particulars to be submitted in addition to those required in Pt 5, Ch 2, 1.4 Submission requirements 1.4.1.
Table 2.15.1 Plans and particulars to be submitted
| Document
|
For
information
(X indicates required submission)
|
For
appraisal
|
| For both DF and GF engines:
|
- Schematic layout or other equivalent
documents of gas system on the engine
|
|
X
|
- Gas piping system (including
double-walled arrangement where applicable)
|
|
X
|
- Parts for gas admission system,
see Note 1
|
|
X
|
- Arrangement of explosion relief valves
(crankcase, see Note 2), charge air manifold, exhaust
gas manifold) as applicable
|
|
X
|
- List of certified safe equipment and
evidence of relevant certification
|
|
X
|
- Safety concept, see Note 3
|
X
|
|
- Report of the risk analysis, see
Note 4
|
X
|
|
|
|
X
|
|
| For DF engine only:
|
- Schematic layout or other equivalent
documents of fuel oil system (main and pilot fuel systems)
on the engine
|
|
X
|
- Shielding of high pressure fuel pipes
for pilot fuel system, assembly
|
|
X
|
- High pressure parts for pilot fuel oil
injection system, see Note 1
|
|
X
|
| For GF engine only:
|
|
|
|
X
|
|
Note 1. The documentation to contain specification of pressures,
pipe dimensions and materials.
|
15.2.2 Where considered necessary to verify the requirements of this Chapter have been
satisfied, LR may request further documents to be submitted.
15.3 Risk analysis
15.3.1 A risk analysis shall be carried out by the engine manufacturer to:
- identify any reasonably foreseeable normal and abnormal
failures which may lead to the presence of gas in components or locations not
designed for such purpose;
- evaluate the consequences including rupture, fire or
explosion;
- identify the failure detection method where necessary;
- identify the corrective measures where the risk cannot be
eliminated:
- in the system design, such as redundancies and
safety devices, monitoring or alarm provisions which permit restricted
operation of the system;
- in the system operation, such as, but not limited
to, initiation of the redundancy and activation of an alternative mode
of operation.
15.3.2 Risk analysis shall be undertaken to a recognised standard, e.g. ISO
31010 Risk management – Risk assessment techniques, and documented in
accordance with LR’s ShipRight Procedure Risk Based Certification (RBC).
15.3.3 Only single failures shall be considered at one time. Both detectable and
non-detectable failures shall be considered. Failures of any component directly
caused by a single failure of another component shall also to be considered (i.e.
consequence failures).
15.3.4 The risk analysis for the engine is to include, but not be limited to:
- failure of the gas-related systems or components, in
particular, gas piping and its enclosure, where provided, and cylinder gas
supply valves. It shall be noted that failures of the gas supply components not
located directly on the engine, such as valves and other components of the gas
valve unit (GVU), are not to be considered in the analysis.
- failure of the ignition system (fuel oil pilot injection or
sparking plugs).
- failure of the air to fuel ratio control system (charge air
by-pass, gas pressure control valve, etc.).
- for engines where gas is injected upstream of the
turbocharger compressor, failure of a component likely to result in a source of
ignition (hot spots).
- failure of the gas combustion or abnormal combustion
(misfiring, knocking).
- failure of the engine monitoring, control and safety
systems. Where engines incorporate electronic control systems, a Failure Mode
and Effects Analysis (F.M.E.A) is to be carried out in accordance with Note 10
in Table 2.1.1 Plans and particulars to be
submitted.
- abnormal presence of gas in engine components (e.g. air
inlet manifold and exhaust manifold of DF or GF engines) and in the external
systems connected to the engines (e.g. exhaust duct).
- changes of operating modes for DF engines.
- hazard potential for crankcase fuel gas accumulation, for
engines where the underside of the piston is in direct communication with the
crankcase, see
Rules and Regulations for the Classification of Ships using Gases or other Low-flashpoint Fuels, July 2022
Pt A-1, 10.3 Regulations for internal combustion engines of piston type
10.3.1.2.
15.3.5 The risk analysis for the engine shall also take into account the impact of the
following external events:
- a gas leakage downstream of the GVU. The GVU is a set of
manual shut-off valves, actuated shut-off and venting valves, gas pressure
sensors and transmitters, gas temperature sensors and transmitters, gas pressure
control valve and gas filter used to control the gas supply to each gas
consumer. It also includes a connection for inert gas purging.
- the safety of the engine in case of an externally activated
emergency shutdown or blackout, when running on gas;
- the interactions between the gas fuel system and the engine;
- failures in systems external to the engine that impact safe
engine operation, such as ship fuel storage or fuel gas supply systems. This may
require action from the engine control and monitoring system in the event of an
alarm or fault condition.
15.4 Design requirements
15.4.1 The allowable gas composition limits for the engine and the minimum and (if
applicable) maximum methane number shall be specified by the manufacturer.
15.4.2 Components containing or likely to contain gas shall be designed to:
- minimise the risk of fire and explosion so as to demonstrate
an equivalent level of safety to an oil-fuelled engine;
- mitigate the consequences of a possible explosion, through
adequate strength of the component(s) or the fitting of suitable pressure relief
devices of an approved type.
See:
15.4.3 Discharge from pressure relief devices shall prevent the passage of flame to the
machinery space and be arranged such that the discharge does not endanger personnel
or damage other engine components or systems.
15.4.4 Relief devices shall be fitted with a flame arrester,
See:
15.5 Gas piping
15.5.1 Engine-mounted gas piping shall be designed in accordance with:
15.5.2 Pipes and equipment on the engine containing fuel gas are to be considered as
hazardous area Zone 0, whereas the space between the gas fuel piping and the wall of
the outer pipe or duct is defined as hazardous area Zone 1,
See:
15.5.3 Double wall gas piping systems on the engine are to be arranged in accordance with:
15.5.4 Double wall pipes or ducts are to be designed in accordance with:
15.5.5 For a ventilated double wall gas pipes on the engine, the ventilation inlet shall be
located in accordance with:
15.5.6 The pipe or duct is to be pressure tested to ensure gastight integrity and to show
that it can withstand the expected maximum pressure at gas pipe rupture in
accordance with:
15.5.7 Single wall piping is only acceptable for engines intended to be installed in
emergency shutdown (ESD)-protected machinery spaces or an appropriate ducting
arrangement provided, in accordance with:
15.6 Charge air system
15.6.1 The charge air system on the engine shall be designed in accordance with:
15.6.2 Engines designed for single engine installations providing power for propulsion or
other essential services shall be capable of continued operation after opening of
the pressure relief valves. LR is to be advised of any reduction in output power
following such an event which is to be stated in the operating manuals.
15.7 Exhaust system
15.7.1 The exhaust gas system on the engine shall be designed in accordance with:
15.7.2 Single engine installations are to comply with:
15.8 Crankcase
15.8.1 Crankcase explosion relief valves shall be installed in accordance with:
15.8.2 For maintenance purposes, a connection, or other means, shall be provided for
crankcase inerting, and ventilating and gas concentration measurement.
15.9 Gas ignition in the cylinder
15.9.1 The requirements are as described in:
15.10 Gas admission valves
15.10.1 Gas admission valves, which control gas supply to the
cylinder(s) according to the cylinder’s (cylinders’) actual gas demand. They
shall be suitably certified safe for use in zone 1. Where gas admission valves
are not rated for zone 1 use, it shall be documented that they are suitable for
safe use in the proposed application. Documentation and analysis is to be based
on IEC 60079-10-1 or IEC 60092-502. Evidence of suitability is to be submitted
for consideration.
15.11 DF engines
15.11.1 DF engines shall be arranged to use either fuel oil or gas fuel for the main fuel
charge and with pilot fuel oil for ignition. They are to be arranged for immediate
changeover from gas use to fuel oil use. In the case of changeover to either fuel
supply, the engines are to be capable of continuous operation using the alternative
fuel supply without interruption to the supply of power.
15.11.2 Changeover to from fuel oil to gas shall be only possible at a power level where it
can be done reliably and safely as demonstrated through testing.
15.11.3 Changeover from gas to fuel oil shall always be possible at all power levels.
15.11.4 Changeover from and to gas operation shall be automatic but manual interruption shall
always be possible.
15.11.5 In case of a gas shut-off, the engines shall be capable of continuous operation on
fuel oil only.
15.11.6 Gas admittance to the combustion chamber shall not be possible without operation of
the pilot oil injection. Pilot oil injection shall be monitored using fuel oil
pressure and combustion parameters.
15.12 GF engines
15.12.1 In case of failure of the spark ignition, the engine is to be shut down unless the
failure can be limited to one cylinder, in which case the gas supply to the affected
cylinder is to be immediately shut-off, the reliability and safety of which is to be
considered in the risk analysis and demonstrated through testing.
15.13 Pre-mixed engines
15.13.1 Inlet manifolds, turbochargers, charge air coolers, etc. are to be
regarded as parts of the fuel gas supply system. Failures of these components are
likely to result in a gas leakage and are to be considered in the risk analysis
(see
Pt 5, Ch 2, 15.3 Risk analysis).
15.13.2 Flame arresters are to be installed before each cylinder head, unless otherwise
justified in the risk analysis, considering the design parameters of the engine
including, but not limited to, the gas concentration in the charge air system and
the path length of the gas-air mixture in the charge air system.
15.14 Control, monitoring, alarm and safety systems
15.14.1 The engine control system is to be independent and separate from the safety
system.
15.14.2 The gas supply valves are to be controlled by the engine control system or by the
engine gas demand.
15.14.3 Combustion is to be monitored on an individual cylinder basis. Where poor combustion
is detected on an individual cylinder, gas operation is to be allowed in accordance
with the conditions specified in:
Where monitoring of combustion for each individual cylinder is not practicable due to
engine size and design, common combustion monitoring will be subject to
consideration by LR.
15.14.4 Unless the risk analysis required in Pt 5, Ch 2, 15.3 Risk analysis proves otherwise, the
monitoring and safety system functions for DF or GF engines are to be provided in
accordance with Table 2.15.2 Monitoring and safety system functions for DF and GF engines in addition to the general monitoring and
safety system functions given in:
For DF engines, Table 2.15.2 Monitoring and safety system functions for DF and GF engines shall only be applied to gas mode.
Table 2.15.2 Monitoring and safety system functions for DF and GF engines
| Parameter
|
Alarm
|
Automatic
activation of the double block and bleed valves
|
Automatic
switching over to fuel oil mode (see Note 1)
|
Engine
shutdown
|
| Abnormal
pressures in the gas fuel supply line
|
X
|
X
|
X
|
X
(see Note 5)
|
| Gas fuel supply
systems – malfunction
|
X
|
X
|
X
|
X
(see Note 5)
|
| Pilot fuel
injection or spark ignition systems – malfunction
|
X
|
X (see
Note 2)
|
X
|
X
(see Notes 2 and 5)
|
| Exhaust gas
temperature after each cylinder – high
|
X
|
X
(see Note 2)
|
X
|
X
(see Notes 2 and 5)
|
| Exhaust gas
temperature after each cylinder, deviation from average – low
(see Note 3)
|
X
|
X
(See Note 2)
|
X
|
X
(see Notes 2 and 5)
|
| Cylinder pressure
or ignition – failure, including misfiring, knocking and unstable
combustion
|
X
|
X(see
Notes 2 and 4)
|
X(see Note
4)
|
X(see
Notes 2, 4 and 5)
|
| Oil mist
concentration in crankcase or bearing temperature– high (see
Note 6)
|
X
|
X
|
|
X
|
| Pressure in the
crankcase – high(see Note 4)
|
X
|
X
|
X
|
|
| Engine stops –
any cause
|
X
|
X
|
|
|
| Failure of the
control-actuating medium and bleed valves
|
X
|
X
|
X
|
|
|
Note 1. DF engine only, when running in gas mode.
Note 2. For GF engines, the double block-and-bleed valves and the
engine shutdown may not be activated in case of specific
failures affecting only one cylinder, provided that the
concerned cylinder shall be individually shut off, and the safe
operation of the engine in such conditions is demonstrated by
the risk analysis.
Note 3. Required only if necessary for the detection of
misfiring.
Note 4. In the case where the failure can be corrected by an
automatic mitigation, only the alarm may be activated. If the
failure persists after a given time, the safety actions are to
be activated. The time period to activate safety actions shall
be demonstrated to LR.
Note 5. GF engine only.
|
|