DESIGN AND INVESTIGATION OF AN ELECTRONIC CONTROL SYSTEM FOR DIESEL-BASED GAS ENGINE CONVERSIONS

ABSTRACT

This research focuses on an electronic microprocessor-based control system for spark-ignition internal combustion engines operating on liquefied petroleum gas (LPG). The system includes two main subsystems: a common-rail LPG injection unit and a contactless ignition system with a movable voltage distributor. It also features a subsystem that manages cylinder filling through a throttle valve and an idle speed regulator with a conical damper. The system supports group or sequential LPG injection near the intake valves, depending on the software. It is suitable for converting both new and existing diesel engines to gas operation, aiming to reduce fuel costs and emissions. A prototype engine, the D-240-LPG-"B", was developed based on the D-240 diesel engine. Its compression ratio was lowered by converting its combustion chamber to an open, truncated cone shape. For optimal control, the Avenir Gaz 37 "B" microprocessor unit was created. Tests confirmed the system’s efficiency and reliability.

АННОТАЦИЯ

В данном исследовании рассматривается электронная микропроцессорная система управления для газовых двигателей внутреннего сгорания с искровым зажиганием, работающих на сжиженном нефтяном газе (СНГ). Система включает два основных подсистемы: аккумулятивную систему впрыска СНГ типа common rail и бесконтактную систему зажигания с подвижным распределителем напряжения. Также предусмотрена подсистема регулирования наполнения цилиндров с дроссельной заслонкой и регулятором холостого хода с коническим демпфером. В зависимости от программного обеспечения, система обеспечивает групповой или последовательный впрыск СНГ возле впускных клапанов. Она подходит для переоборудования как новых, так и уже используемых дизельных двигателей, снижая эксплуатационные затраты за счёт замены дизельного топлива на более дешёвый и экологически чистый газ. Для проверки эффективности была разработана модель газового двигателя D-240-LPG-"B" на базе дизельного двигателя D-240. Степень сжатия была снижена за счёт изменения камеры сгорания на открытую, осесимметричную, усечённого конуса. Для управления всеми подсистемами был создан блок управления Avenir Gaz 37 "B". Испытания подтвердили эффективность микропроцессорной системы управления.

Keywords: gas engine, gas engine control system, electronic control unit, liquefied petroleum gas.

Ключевые слова: газовый двигатель, система управления, микропроцессор, сжиженный нефтяной газ.

Introduction

Many researchers and companies around the world [3; 4; 13] are working on converting transport diesel engines into spark-ignition internal combustion engines (ICEs) running on gaseous fuels. A key aspect of these conversions is how to reduce the compression ratio of the diesel engine.There are three main approaches:

1. Installing additional cylinder head gaskets [3; 4], which worsens environmental performance.
2. Applying the Miller thermodynamic cycle, which reduces the actual rather than geometric compression ratio [9; 11], but retains the diesel-type combustion chamber and doesn't fully solve efficiency and emissions issues.
3. The most common method — increasing the combustion chamber volume to reduce the actual compression ratio [1; 2; 10], with variations depending on chamber design [6].

Another major distinction in conversions is the choice of gaseous fuel: compressed natural gas (CNG) or liquefied petroleum gas (LPG). While most conversions use CNG, its heavy storage tanks reduce vehicle capacity. In contrast, LPG offers energy density close to gasoline and diesel and does not require significant vehicle modification. LPG vehicle usage has grown significantly worldwide, exceeding 25 million units [14]. Therefore, this research focuses on an electronic microprocessor control system for gas ICEs running on LPG. The goal is to develop and investigate a system with the Avenir Gaz 37 "B" ECU, supporting both group and sequential LPG injection.

Materials and methods

The study involved:

– Non-motorized testing of the Avenir Gaz 37 "B" electronic control unit (ECU) on a specially developed modeling stand;

– Bench (motor) testing of the electronic microprocessor control system integrated into the D-240-LPG-"B" gas engine. To commission the Avenir Gaz 37 "B" ECU, a dedicated modeling stand was designed and built. It included input sensors and actuators used in a 4-cylinder gas engine control system. Input sensors comprised:–

Crankshaft speed and angle sensor, and the Hall sensor of the distributor (simulated by pulse generators);

– Throttle valve position sensor;

– Coolant temperature sensor. Actuators and stand devices included:

– A Common Rail gas rail with four low-resistance electromagnetic injectors;

– Three solenoid valves (in the reducer-evaporator, the gas cylinder multivalve, and the LPG filter valve);

– An idle speed regulator. All components of the fuel system and LPG injection system (group or sequential) met standards [5; 12]. To reduce the compression ratio of the D-240 diesel engine (ε = 16), the third method was applied—transforming the semi-closed TsNIDI-type combustion chamber into an open, axisymmetric “truncated cone” shape with a new ratio of ε = 9.5 [6]. Bench tests of the gas engine D-240-LPG-"B" with the Avenir Gaz 37 "B" ECU were conducted using a Zöllner B-350AS electric load stand (Germany).

                                      a                                                         b                   

Figure 1. Photo of a gas internal combustion engine (ICE)  D-240-LPG-«B» installed on a Zllner electric load stand  of the B-350AS type: a– gas ICE at the stand; b– gas cylinder  for supplying a gas ICE with liquefied petroleum gas

The stand is equipped with a modernized microprocessor-based measurement and control system that measures, calculates, and records all necessary gas engine parameters for bench testing, along with environmental conditions in the test chamber.

Results and discussion

A multifunctional microprocessor-based ECU Avenir Gaz 37 “B” was developed and manufactured to control the gas engine operation (Fig. 2). The engine was equipped with three subsystems:

– an accumulative power supply subsystem and multipoint injection using LPG electromagnetic gas nozzles;

– a contactless electronic ignition subsystem (CEIS) with a movable voltage distributor;

– a subsystem for controlling the filling of the cylinders with the working mixture.

a                                        b                                            c

Figure 2. Multifunctional microprocessor electronic control unit (ECU)  Avenir Gaz 37 «В»: a– Avenir Gaz 37 «В» board assembled;  b– ECU appearance; c– wiring harnesses for connecting  the control unit with sensors and devices

The ECU Avenir Gaz 37 “B” is based on a high-performance 16-bit PIC24F microcontroller (Microchip Technology Inc.) with nanoWatt XLP technology, which ensures ultra-low power consumption. The unit includes advanced energy-saving features, including low voltage mode. The maximum clock frequency is 32 MHz, and its processing power reaches 16 DMIPS at this frequency. Non-motorized tests of the Avenir Gaz 37 “B” ECU confirmed its operability and showed that its performance is sufficient to manage gas engine operation in real time. Bench tests of the D-240-LPG-“B” gas engine equipped with the developed electronic microprocessor control system and the Avenir Gaz 37 “B” ECU confirmed the ability to implement both group and sequential LPG injection. The principles of operation for group LPG injection with the Avenir Gaz 37 “B” ECU are described in [8]. A key innovation in this system is the electronic communication between the ECU and the distributor’s Hall sensor, allowing the system to function reliably even in case of failure of the engine speed sensor. For sequential injection, described in [7], the system can operate without a camshaft position sensor or special master disk on the camshaft. This was achieved by modifying the ignition system—specifically, the standard master disk (obturator) of the distributor was altered by extending the arc length of the opening for the first cylinder. As a result, the ECU receives a signal from the Hall sensor indicating the piston’s position in the first cylinder relative to top dead center.

Tests showed that the control system performs the following main and additional functions:

– precise dosing of gas fuel into each ICE cylinder;

– regulating the amount of startup fuel depending on engine coolant temperature;

– regulating idle speed based on coolant temperature;

– limiting maximum engine speed by forming an external control characteristic, etc.

Bench tests of the D-240-LPG-"B" gas engine with the ECU confirmed efficient operation. According to the World LPG Association (WLPGA) [14], LPG is the most widely used alternative motor fuel in the world. Considering its widespread use and low cost, converting diesel engines to gas ICEs is an effective way to reduce vehicle operating costs.

Conclusion

The justification for converting diesel vehicle engines into gas internal combustion engines (ICEs) with forced ignition to run on LPG has been demonstrated. A microprocessor-based electronic control system for gas ICEs with spark ignition has been developed. As part of this system, a special multifunctional electronic control unit—Avenir Gaz 37 "B"—was designed and manufactured. Depending on the software version, the ECU is capable of performing either group or sequential LPG injection. It has been confirmed that converting diesel engines to gas ICEs is an effective method for reducing the operating costs of diesel powered vehicles.

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