In the late 70s, the bulk of the new trucks of the USSR were cars equipped with gasoline engines. The production of diesel trucks was only gaining momentum and was carried out at the only plant in Naberezhnye Chelny. As an alternative solution, GAZ and ZIL plants began to develop modifications of vehicles adapted to work on compressed or liquefied gas.
Liquefied gas was noticeably cheaper than gasoline and could provide a significant reduction in exhaust emissions. Gas trucks were used in large enough cities equipped with special gas stations. Another place of application of such machines was the fleet of oil and gas exploration.
Based on ZIL-130
One of these vehicles was the ZIL 138 airborne vehicle, which was a gas-cylinder modification of the Model 130 truck. The main fuel used was a mixture of liquefied petroleum gases - propane and butane. The engine had a backup system for supplying gasoline A76, which was used for starting and warming up. Serial production of machines began in 1977 and continued until 1986. The exact number of machines manufactured is not known, since the plant produced a set of parts for the conversion of machines. Such work was carried out by the fleets themselves. An early prototype liquefied gas truck in the photo.
One of the main differences was the installation of a specialized engine with an increased degree of compression and special devices providing fuel supply. Externally, the car is easy to distinguish by the installed gas cylinder in bright red. A cylinder with a volume of 225 liters was located on the left side member of the frame, in place of the standard 150-liter gas tank. Liquefied gas was in a cylinder under a pressure of 16 atm. On the cylinder there was a special valve for refueling and a safety device. Gas level control was carried out by a special sensor. The installation of gas supply equipment increased the curb weight and gross weight of the cargo truck by 115 kg.
Modifications
On the basis of the ZIL-138 gas balloon vehicle , a whole family of cars was created. An airborne version with a 3800 mm standard wheelbase could be shipped to customers in the form of a bare chassis for installing various specialized add-ons. In addition to the base machine, the most common were the tractor unit under the designation 138B1 and the chassis for the manufacture of construction dump trucks 138D2. These options had a shortened to 3,300 mm wheelbase and two cylinders for liquefied gas. Cylinders have a volume reduced to 117.4 liters and are located behind the cab on the frame side members.
The tipper chassis was slightly different with additional options. Among them were a modified brake valve and a towing hook with adjacent connectors for connecting the trailer's electrical and pneumatic systems. Such a chassis served as the basis for the MMZ 45023 dump truck. The truck tractor could be operated with various types of semi-trailers with a gross weight of not more than 14,000 kg.
Features of the power plant
The eight-cylinder V-engine of the Soviet ZIL 138 truck was based on the standard model 130 gasoline engine. The main type of fuel was the so-called “technical propane” or “liquefied petroleum gas”, which had a standard composition and was produced by oil refineries. The compression ratio was increased to 8 units (from 6.5 on the 130th motor), which made it possible to maintain power and traction characteristics at the level of gasoline counterparts. Serial ZIL-138 - in the photo below.
Fuel supply
On a gasoline engine, a carburetor is used to prepare the mixture, which is not suitable for supplying gas. The initial stage of preparation of the fuel mixture is the conversion of fuel from the liquid phase to the gaseous state. The gas in the cylinder is in liquid and gaseous state. The mixture of gas phases enters the main pipelines through the supply valves. Each gas phase had its own valve. Having passed through the main valve, the gas is filtered from mechanical particles and suspended solids. The replaceable felt filter is made in one housing with an electromagnetic valve and is installed on the motor partition of the cab.
Then the gas enters a special evaporator, where it completely passes into a gaseous state. The evaporator was located in the intake manifold of the engine and had heating from the cooling system. After that, the fuel enters the first stage of the gas reducer. In front of the first gearbox chamber there is an additional filter with a replaceable element. The pressure reducer is a two-stage pressure regulator. Rubberized diaphragms are installed inside the gearbox, mechanically connected with control valves. Gas passing through the stages of the gearbox reduces its pressure to the required level. The pressure in the first chamber of the gearbox is displayed on a pressure gauge mounted on the dashboard of the machine.
Additionally, in the second chamber of the gearbox there is a device that dispenses the fuel supply depending on the engine speed. The design of the device has a special solenoid valve that supplies a portion of gas to the mixer when starting a cold engine. The valve opens with a button from the driver's seat.
Propane passing through the gearbox enters a mixer mounted directly on the engine. The mixer is actually a carburetor of a special design, which provides a mixture of air and gas and its supply to the engine cylinders. The mixer is equipped with a speed limiter and heating from the engine cooling system.
A horizontal carburetor is installed next to the mixer for a backup gasoline supply system. In the design of a gasoline carburetor, there are two flame arresters made of metal mesh. Gas is supplied by a pump from a separate 10-liter tank installed under the cab floor on the right side.
Compressed gas
In 1982, the base truck of the plant underwent a major modernization aimed at improving operational and technical characteristics. ZIL 138 was finalized in a similar way. The base car was optionally equipped with an engine with the ability to work on compressed gas. Such a motor was equipped with a unified cylinder head with a compression ratio of 6.5. Because of this, the power of the power unit did not exceed 120 forces. The onboard chassis was produced in two forms:
- with a standard base of 3800 mm and a carrying capacity of 5200 ... 5400 kg (138A);
- with an elongated base of 4500 mm and a lifting capacity of 5000 ... 5300 kg (138AG).
On special orders, the ZIL-138I variant was delivered with a standard base, equipped with a cylinder head engine with a compression ratio of 8 units. The motor developed up to 135 forces when working on gas or up to 160 forces on AI93 gasoline. The variant with an extended base bore the ZIL-138IG index. You can see the general view of the model with gas cylinders in the photo below.
Gas was in eight 50-liter cylinders mounted across the frame. For safety, the cylinders were divided into two groups, for each of which there was a separate valve for supplying gas. With the start of production 138A, all gas trucks of the ZIL plant received a heightened front side of the platform. This refinement slightly increased the safety of the cab when the truck capsized. Compressed gas vehicles had a standard 150-liter gas tank.
Small batch and experienced
In addition to liquefied gas vehicles, there were options designed to operate on compressed gas. All machines were developed and tested in the early 80s.
Such were the experimental ZIL-138AB and 138AV, which had a standard base and equipped with eight cylindrical cylinders for storing fuel. The motors of the machines developed a capacity of up to 120 liters. from. Another prototype was the ZIL-138IB, which had a long base and a 135-horsepower engine with an increased compression ratio.