FASUNIT-2LEC-3

PROF. KUNALSINHMECHANICAL ENGINEERING

LPG ENGINE

INTRODUCTION OF LPG Autogas is the common name for liquefied petroleum gas (LPG) when it is

used as a fuel in internal combustion engines in vehicles as well as instationary applications such as generators. It is a mixture of propane andbutane.

Autogas is widely used as a "green" fuel, as it decreases exhaust emissions.In particular, it reduces CO2 emissions by around 35% compared to petrol.One litre of petrol produces 2.3 kg of CO2 when burnt, whereas theequivalent amount of autogas produces only 1.5 kg of CO2 when burnt.Ithas an octane rating (MON/RON) that is between 90 and 110 and anenergy content (higher heating value—HHV) that is between 25.5megajoules per litre (for pure propane) and 28.7 megajoules per litre (forpure butane) depending upon the actual fuel composition.

Autogas is the third most popular automotive fuel in the world, withapproximately 16 million of 600 million passenger cars powered using thefuel, representing less than 3% of the total market share. Approximatelyhalf of all autogas-fueled passenger vehicles are in the five largest markets(in ascending order): Turkey, South Korea, Poland, Italy, and Australia.

SYSTEM COMPONENTS

FILLER The fuel is transferred into a vehicle tank as liquid by

connecting the bowser at the filling station to the filler fittingon the vehicle.

The type of filler used varies from country to country and insome cases different types are used within the same country.

The three types are:◦ ACME thread. This type has a threaded fitting onto which the

bowser nozzle is screwed before the trigger is pulled toestablish a seal before fuel transfer. This type is used in Australia,USA, Germany, Austria, Belgium, Republic of Ireland.

◦ 'Dutch' Bayonet. This type establishes a gas proof seal by a pushand twist action. This type is used in the United Kingdom,Netherlands and Switzerland.

◦ 'Italian' Dish. This type is used in Italy, France, Poland, Scandinaviaand Portugal.

FILLER LOOKS

Hoses, pipes and fittings The hose between the filler and tank(s) is called

the fill hose or fill line. The hose or pipe betweenthe tank(s) and the converter is called the serviceline. These both carry liquid under pressure.

The flexible hose between the converter andmixer is called the vapour hose or vapour line.This line carries vapour at low pressure and has amuch larger diameter to suit.

Where the tank valves are located inside anenclosed space such as the boot of a sedan, aplastic containment hose is used to provide a gas-tight seal between the gas components and theinside of the vehicle.

CONT.. Liquid hoses for LPG are specifically designed and

rated for the pressures that exist in LPG systems,and are made from materials designed to becompatible with the fuel. Some hoses are madewith crimped fittings, while others are made usingre-usable fittings that are pressed or screwedonto the end of the hose.

Rigid sections of liquid line are usually made usingcopper tubing, although in some applications, steelpipes are used instead. The ends of the pipes arealways double-flared and fitted with flare nuts tosecure them to the fittings.

HOSES ,PIPES LOOK

TANK

The tanks have fittings for filling, liquidoutlet, emergency relief of excesspressure, fuel level gauge and sometimes avapour outlet. These may be separatevalves mounted into a series of 3 to 5holes in a plate welded into the tank shell,or may be assembled onto a multi-valveunit which is bolted into one large holeon a boss welded into the tank shell.

CONT Modern fill valves are usually fitted with an automatic

fill limiter (AFL) to prevent overfilling. The AFL has afloat arm which restricts the flow significantly butdoes not shut it off entirely. This is intended to causethe pressure in the line to rise enough to tell thebowser to stop pumping but not cause dangerouslyhigh pressures. Before AFLs were introduced, it wascommon for the filler (with integral check valve) tobe screwed directly into the tank, as the operator hadto open an ullage valve at the tank while filling,allowing vapour out of the top of the tank andstopping filling when liquid started coming out of theullage valve to indicate that the tank was full. Moderntanks are not fitted with ullage valves.

CONT.. The emergency pressure relief valve in the tank is

called a hydrostatic pressure relief valve. It isdesigned to open if the pressure in the tank isdangerously high, thus releasing some vapour tothe atmosphere to reduce the pressure in thetank. The release of a small quantity of vapourreduces the pressure in the tank, which causessome of the liquid in the tank to vaporise to re-establish equilibrium between liquid and vapour.The latent heat of vaporisation causes the tank tocool, which reduces pressure even further.

TANK

VALVES There are a number of types of valve used in autogas

systems. The most common ones are shut-off or filter-lockvalves, which are used to stop flow in the service line. Thesemay be operated by vacuum or electricity. On bi-fuel systemswith a petrol carburettor, a similar shut-off valve is usuallyfitted in the petrol line between the pump and carburettor.

Check valves are fitted in the filler and on the fill input to thefuel tank to prevent fuel flowing back the wrong way.

Service valves are fitted to the outlet from the tank to theservice line. These have a tap to turn the fuel on and off. Thetap is usually only closed when the tank is being worked on.In some countries, an electrical shut-off valve is built into theservice valve.

CONT.. Where multiple tanks are fitted, a combination of

check valves and a hydrostatic relief valve areusually installed to prevent fuel from flowing fromone tank to another. In Australia, there is acommon assembly designed for this purpose. It isa combined twin check valve and hydrostaticrelief valve assembly built in the form of a T-fitting,such that the lines from the tanks come into thesides of the valve and the outlet to the convertercomes out the end. Because there is only onecommon brand of these valves, they are knowncolloquially as a Sherwood valve.

VALVES

CONVERTER The converter (also known as vaporiser) is a device designed

to change the fuel from a pressurised liquid to a vapour ataround atmospheric pressure for delivery to the mixer orvapour phase injectors. Because of the refrigerantcharacteristic of the fuel, heat must be put into the fuel bythe converter. This is usually achieved by having enginecoolant circulated through a heat exchanger that transfersheat from that coolant to the LPG.

There are two distinctly different basic types of converterfor use with mixer type systems. The European style ofconverter is a more complex device that incorporates an idlecircuit and is designed to be used with a simple fixed venturimixer. The American style of converter is a simpler designwhich is intended to be used with a variable venturi mixerthat incorporates an idle circuit.

CONT.. Engines with a low power output such as; scooters, quad

bikes and generators can use a simpler type of converter(also known as governor or regulator). These converters arefed with fuel in vapour form. Evaporation takes place in thetank where refrigeration occurs as the liquid fuel boils. Thetanks large surface area exposed to the ambient airtemperature combined with the low power output (fuelrequirement) of the engine make this type of system viable.The refrigeration of the fuel tank is proportional to fueldemand hence this arrangement is only used on smallerengines. This type of converter can either be fed with vapourat tank pressure (called a 2 stage regulator) or be fed via atank mounted regulator at a fixed reduced pressure (called asingle stage regulator).

MIXER

The mixer is the device that mixes thefuel into the air flowing to the engine. Themixer incorporates a venturi designed todraw the fuel into the airflow due to themovement of the air. Mixer type systems have existed since the

1940s and some designs have changedlittle over that time. Mixers are now beingincreasingly superseded by injectors.

MIXER

INJECTORS VAPOUR PHASE INJECTORS:

◦ Most vapour phase injection systems mount thesolenoids in a manifold block or injector rail, thenrun hoses to the nozzles, which are screwed intoholes drilled and tapped into the runners of theintake manifold. There is usually one nozzle foreach cylinder. Some vapour injection systemsresemble petrol injection, having separateinjectors that fit into the manifold or head in thesame manner as petrol injectors, and are fed fuelthrough a fuel rail.

INJECTORS

Liquid phase injectors◦ Liquid phase injectors are mounted onto the

engine in a manner similar to petrol injectors,being mounted directly at the inlet manifoldand fed liquid fuel from a fuel rail.

INJECTORS (VAPOUR)

Electrical and electroniccontrols

There are four distinct electrical systemsthat may be used in autogas systems - fuelgauge sender, fuel shut-off, closed loopfeedback mixture control and injectioncontrol. In some installations, the fuel gauge sender

fitted to the autogas tank is matched to theoriginal fuel gauge in the vehicle. In others,an additional gauge is added to display thelevel of fuel in the autogas tank separatelyfrom the existing petrol gauge.

CONT.. Closed loop feedback systems use an electronic

controller that operates in much the same way as in apetrol fuel injection systems, using an oxygen sensorto effectively measure the air/fuel mixture bymeasuring the oxygen content of the exhaust andcontrol valve on the converter or in the vapour lineto adjust the mixture. Mixer type systems that do nothave a closed loop feedback fitted are sometimesreferred to as open loop systems.

Injection systems use a computerised control systemwhich is very similar to that used in petrol injectionsystems. In virtually all systems, the injection controlsystem integrates the tachometric relay and closedloop feedback functions.

Thank you

Kunalsinh Mechanical engineering department.