Characteristics:
- Engine: 6 cylinders in-line turbocharged
- Displacement: 9,5 l
- Bore x stroke: 120x140 mm
- Compression rate: 9:1
- Combustion chamber: Bowl in piston
- Rated power: 154 kW at 2000 rpm
- Maximum efficiency: 0.36
- Overlap angle: 0
- Fuel feeding system: pressure reducer and Venturi mixer
- Ignition system: one coil per cylinder
The original Diesel engine was acquired by Istituto Motori in 1989, already modified for gas-controlled ignition operation, through the following interventions:
- reduction of the volumetric compression ratio from 17 to 10:1;
- removal of the diesel fuel system;
- modification of the cylinder head with replacement of the valves to increase the operating temperatures and adaptation of the sleeve to house the spark plug and sealing elements to avoid water passage into the cylinder head;
- installation of the gas supply system with pressure reducer and Venturi mixer.
Subsequently, the engine was further modified in the Institute with various interventions:
- replacement of the original camshaft (50° valve crossover) with one expressly designed for spark ignition operation (zero crossover);
- installation of the high-performance electronic ignition system, with the possibility of varying the ignition advance angle;
- replacement of the gas supply system with Venturi mixer, with subsequent developments including electronic control of the gas flow rate regulation valve (stepper motor) and subsequent implementation of a phased multipoint supply system;
- replacement of the supercharging unit with one with a lower boost pressure, in order to maintain in gas operation with spark ignition in stoichiometric conditions, the same performance as the diesel version;
- subsequent evolution with higher boost pressure for operation with lean mixtures (lean burn), with modification of the Wastegate valve to allow regulation of the boost pressure, depending on the operating conditions.
In subsequent versions the engine was tested both with a trivalent catalyst and with an oxidation-only catalyst for the lean burn version. The experimental activity, conducted in the early nineties, led to the approval of the first urban bus prototype powered by natural gas for the city of Florence.
This activity also formed the basis for decades-long activities on gas engines in general, both with spark ignition and dual fuel, both with natural gas and with natural gas and hydrogen mixtures, including among these also ternary mixtures containing high nitrogen fractions, for simulate the composition of syngas.